I would say this perception is based both on very limited understandings of Platonic and Confucian thought and on an overeagerness to assign fixed and unchanging qualities to "the east" and "the west." It also overlooks the ways in which Plato and Confucius were shaped by the realities of their own times- both were original thinkers but were very much a part of broader cultural and intellectual trends. Additionally, I would argue that looking at Confucius as primarily a "philosopher" in the way that Plato was (or, for that matter, like Confucius' successors Mencius or Xunzi were) is basically a misunderstanding of what he thought and why, and of how his "school of thought" was composed. Confucius considered himself an antiquarian and a scholar of traditional Zhou culture; to the extent that he had particular social and ethical views, they grew out of his view of the past.

The first question at hand is whether or not Confucius was more authoritarian than Plato, and if so, in what ways. In answering this question we are partly limited by the nature of the resources we have on hand. Plato wrote a great deal himself and we are able to track the development of many of his ideas over time, but we have no philosophical works attributed to Confucius' own hand (tradition names him as the editor and compiler of some of the "Classics" from old Zhou materials, but these are historical or literary in nature and Confucius himself may not have actually been involved in them anyway). The Analects were compiled after his death by his disciples as a kind of remembrance, not as a comprehensive explanation of his worldview, and later still some works like the Great Learning put words in Confucius' mouth in much the way that Plato may have done to Socrates. Plato's dialogues were written with a clear rhetorical purpose, often dealing with metaphysical concepts like his Theory of Ideas, whereas the Analects have no particular structure, make few direct arguments, and almost entirely evade metaphysical questions in favor of discussions on individual morality, appropriate social relationships, and how a man of superior character should conduct himself in a fallen world. In short, we have much more material from Plato than we do from Confucius, and Plato addressed many questions that Confucius did not. It's also worth noting that the Analects includes passages where Confucius is questioned and even criticized by his students, as well ones in which the master himself does not speak, so it is not accurate to characterize it as a series of maxims to be accepted uncritically.

More to the point, Plato and Confucius both espoused hierarchical social models, which were clearly influenced by the prevailing political conditions of their respective cultures. Here, I'll quote the excellent The World of Thought in Ancient China by Benjamin I. Schwartz:

Leaving aside the troublesome questions of semantics, we have already discerned some of the aspects of Confucius' vision which have led some to see "liberal," "democratic" or "individualistic" tendencies in the Analects. On the "democratic" side, it is first of all clear that good government exists to serve the needs of the people, especially their economic needs... In a good society the people will enjoy a living space of their own in which there will be scope for moral autonomy...

On the side of "individualism," we have the fact that while an individual is linked to his social roles, his behavior is not simply a function of these roles. He has a potential moral autonomy which makes it possible at least for some individuals to realize the full moral potentialities of their roles and to convey to others their full humanity, whether through the framework of the "role structure" or outside of it... If "individualism" refers to something like Kantian moral autonomy, something of it can certainly be found here.

None of this, however, involves any diminution of the strong emphasis on the symbols of hierarchy and authority inherent in the entire system of li... Running quite counter to the emphasis on true merit we also find in the Analects an ongoing positive stress on hereditary prerogative. This has confirmed for many the essentially "reactionary" nature of Confucius' vision. Plato's Republic is after all based on a rigid division of classes yet it remains- despite its recommendation of a eugenics program- a strict meritocracy.

In short, Confucius' beliefs as expounded in the Analects contain elements which have been regarded as "liberal" as well as "reactionary" elements- but the root of the charges of reactionary or authoritarian attitudes basically derive from Confucius' commitment to hereditary monarchy. This position did not originate with Confucius and was not unique to Confucian thought, as even its ideological rivals Legalism, Mohism and Daoism all accepted the principle of hereditary rule. Their precise view of the role or significance of the monarch varied in important ways, but none advocated "republicanism" as such.

Regarding Plato, in his Republic we see a strictly-hierarchical society shaped by eugenics and intensive, specialized indoctrination for the ruling class of "guardians." The only regard in which this vision isn't significantly more "authoritarian" than Confucius' vision in terms of the level of state interference in the lives of individuals is in the lack of hereditary rulership. Corporate government by groups of political equals was the norm in most Greek cities of the time, and Plato's view of "tyranny" reflects the negative view of monarchy that would have been common among many educated Greeks. Which is to say that, just as Confucius did not create or cause Chinese culture's monarchism, Plato did not introduce "republicanism" to a Greek culture which had already been mostly rid of kings for centuries at that point.

Lastly, I'd like to emphasize that Confucianism underwent changes over time which significantly altered the status of "the Master" within the tradition and the influence of the tradition on society as a whole. "Confucianism" itself is a Western term; the Chinese term was not "the school of Confucius" but "the school of scholars/gentlemen," or Rujia 儒家. This school emphasized the study of ancient Zhou texts, the importance of music and ritual, the value of education as a tool for moral improvement and the need for government based on the virtue of ren, often rendered as "humaneness." The Analects and the works of later Confucian philosophers like Mencius and Xunzi were considered secondary in importance to the original Zhou classics for many centuries after the death of Confucius. It was not until the Song dynasty, some 1,500 years later, that the teachings of Confucius and Mencius were elevated to a status above the ancient "five classics" and it becomes more appropriate to think of the Confucians as followers of his own personal teachings rather than as classicists who followed his curriculum.

It should also go without saying that it's hardly possible to pin the causes of recent events down to the different teaching styles of two men who died over two thousand years ago. An awful lot has happened in the meantime.

References:

Benjamin I. Schwartz, The World of Thought in Ancient China

Jacques Gernet, A History of Chinese Civilization

Anthony Kenny, A New History of Western Philosophy: Ancient Philosophy

Simon Leys, trans., The Analects of Confucius