Alright, so to boil it down, you've got two types of dynastic orders in Imperial China - native Han dynasties, and foreign conquest dynasties. And I realize what's to come might seem circuitous, but I do think giving a brief accounting of the overall situation is key to understanding the implications of what you're asking for, so here it goes...
Great Ming was the former - and in fact the last of the former - and with every reason for ethnic Han Chinese to feel proud and loyal to it. It had been the Imperial Zhu Clan that had restored Chinese rule to China following the collapse of the preceding Mongol conquest dynasty, the Yuan, which had seen the Han people effectively locked out of positions of any real authority in favor of Mongols and foreigners. When the Empire of the Great Khan started running out of steam in the mid-14th century, though, it was Zhu Yuanzhang - the eventual founder of the Ming, the Hongwu Emperor - who spearheaded the successful rebellion against the faltering Mongol dynasty.
The order brought to China by the Ming following the chaos that had enveloped it at the time of the anti-Yuan revolt was, in the words of Reischauer, "one of the greatest eras of orderly government and social stability in human history." Though never able to recreate the physical greatness of the high-highs of the Han or the Tang, Ming China was nevertheless a booming period for Chinese culture, progress, and civilization. It is remembered as a period of high art, poetry, music, and a revitalization of opera not seen since the fall of the Song. Not only the "high forms" of art, but many works of fiction that were aimed at the peasantry and "lesser-educated" classes ban to appear as well, many of which remain wildly popular even through today: Journey to the West and Water Margin to name just a couple. In essence, and especially after its fall in in the 17th century, The Ming came to be remembered as the last, great period of Chinese ethnic sovereignty during the Imperial Era.
The Qing, in contrast, was the second foreign conquest dynasty which managed to gain total control over China and thus establish its legitimacy as an actual Chinese dynasty (in contrast to, for instance, Northern Wei of the 16 Kingdoms, since it only ever controlled the north of China). Once again, Han Chinese were subjected to foreign laws from foreign rulers from the northern steppes, this time not Mongols, but the Jurchen Aisan Gioro from Manchuria. This is not to say, for instance, that this was all bad - the Qing outlawed the rather horrific practice of foot-binding of girls, for instance (as had the Mongols before them). One of the other obvious rules implemented by the Jurchen was the mandate of the queue ponytail shortly after the fall of Beijing to the Great Qing. In the words of Spencer, "To keep the hair, you lose the head; To keep your head, you cut the hair." The rationale behind mandating that all Chinese men (monks excepted) must cut their hair in the Manchu fashion was, in essence, a loyalty test to the new regime. Those who refused to do so - citing the millennia-old Confucian stipulation that no hair should ever be cut, since it was a part of the human body, and thus sacred - were enemies of the Qing regime, and thus faced immediate execution.
One of the most infamous mass executions - and an especially important example of why the differentiation between Ming Loyalist and Qing Defector was such a sore point even centuries later - would come about at the hands of ethnically Han defectors, led by a general named Liu Liangzuo. Upon their capture of the city Jiangyin in October 1645 after a siege of some 83 days, General Liu wound up ordering the massacre of virtually the entire population, by some accounts as many as 100,000 people. Such occurrences at the hand of defectors - or as the Han understandably came to view them, traitor to their own race - were not uncommon in the initial period of conquest, and would burrow their way deep into the collective psyche of the Han Chinese.
Such sentiment - the longstanding impotent rage of being oppressed and ruled over by a foreign people - would mutate as the Qing gradually lost power over their own affairs to another group of foreigner in the 19th century - this time the cabal of Western and Western-ish world powers including Britain, Germany, Russia, France, Japan, and to a lesser extent the USA. This would come to be known as the bainian guoche, the Century of Humiliation as China found itself unable to resist as it was effectively carved apart in all but name by empires from half a world away. All of this would at last boil over into the Xinhai Rebellion against the Qing in 1911, at lat doing away with the Imperial Dynastic System altogether and establishing the Republic of China.
But euphoric as that must have been, the new Chinese state - freshly freed of foreign rule and back in the hands of the Han for the first time in almost 300 years - was almost immediately reminded of the fact that foreign powers were still very much interested in reconquering them for their own interests, and no one more so than the Empire of Japan, who had seized control of Korea from the Qing in 1895 during the First Sino-Japanese War, and in 1915 issued the Twenty-One Demands to the Guomindang (KMT) government which, while pretty roundly rejected by both China and the other Western Powers, nevertheless signaled to everyone involved that the Japanese Empire was far from done with its conquest and colonization of China. That would come to a head in 1938 with the outbreak of the Second Sino-Japanese War, which only ended with the end of the Second World War in 1945.
Even then, though - and especially following the fall of the RoC to the PRC a scant 3 years later in 1948 - China remained keenly sensitive to the idea of foreign occupation, or even oversized influence over its laws, culture, or way of life... and keenly aware that they could be sold out by their own blood to the foreigners. Even immediately before the outbreak of the 2nd S-J War, in 1937 the KMT issued a law called the Regulations on Handling Hanjian Cases (chuli hanjian anjian tiaoli). That term, hanjian literally means "traitor to the Han," or "race traitor." From Xia (2013):
promulgated in August 1937, [it] identified collaborators based on their wartime conduct and stipulated punishments regardless of their age, gender, or ethnicity. Popular anti-hanjian discourse, however, paid particular attention to “female collaborators” and deployed a highly gendered vocabulary to attack hanjian suspects of both sexes. Complementing the legal purge of collaborators, such literature brought extreme pressure on individuals targeted as hanjian and influenced how political crimes should be exposed and transposed onto other aspects of social life.
That cultural "sensitivity" to the foreign easily translated into film and pop culture, and even today there is a strong sentiment of distrust toward and hesitance to too closely embrace that which is "other"... even as China has more and more kissed globalization and Westernization full on the mouth. There is always present the paradox that has ever been a part of Chinese foreign policy, whether Tang, Ming, or the modern PRC: the simultaneous push toward openness and intercourse with foreign countries, and the pull of "closing the door" and retaining ethnic and cultural "purity."
So, to sum up: Chinese culture has a rich and old tradition of making historical allusions to its own past in order to "shorthand" a contemporary event into a familiar narrative. The fall of the Ming to the Qing - and especially the fact that many of the massacres against Han civilian populations were perpetrated by Han defectors on behalf of the foreign invaders - left a lasting cultural "meme" that could (and was) resonant in the culture and film even through the 20th century. To call someone a Ming Loyalist means that you are loyal to China and the Han race, while calling someone a Qing Traitor means, in effect, that you are Hanjian - a race traitor and enemy of the nation. Culturally, someone only needs to say those phrases to call back the whole centuries-long idea behind it.
Twitchett, Denis (ed.) (1988). The Cambridge History of China: Volume 7, The Ming Dynasty, 1368–1644, Part 1
Reischauer, E., John K. Fairbank, and Albert M. Craig (1960). A History of East Asian Civilization, Vol 1.
*Spence, Jonathan (2012). The Search for Modern China.
Finally, though we're nowhere near the Ming of Qing yet, may I suggest The History of China Podcast. We're currently in the middle of the An Lushan Rebellion, the 3rd deadliest war in human history 0.o
