So on the one hand, yes, concentration camps existed well before the Nazis began to use them in the 1930s. A number of prominent examples exist, most notably the British during the Second Boer War, but also the Americans in the Philippines and the Spanish in Cuba. On the other hand though, using this as a direct parallel with the Nazi Concentration Camps is something of a minefield that must be tread carefully. I would note that 'Three Arrows' is a solid YT channel - we have even collaborated with them for an AMA - so while I don't have the time to watch that whole thing I would expect that they do a decent job contextualizing this and more likely are pushing back against those who use the term without good context.

The most important thing to understand is just why the Nazi regime called them that. In his excellent history of the Camp systen, Wachsmann gets to the heart of this when he writes that "these were not prototypes of the later SS camps, differing greatly" and further more that attempts to draw parallels by the Nazis were purposefully obfuscating:

The real meaning behind this propaganda - that the SS camps were not exceptional - could hardly be missed, but just to make sure that everyone got the message, SS leader Heinrich Himmler spelled it out during a speech on German radio in 1939. Concentration camps were a "time-honored institution" abroad, he announced, adding that the German version was considerably more moderate than foreign ones.

Although I wasn't writing about the turn-of-the-century camps but rather the contemporary internment of American citizens of Japanese descent, and immigrants from Japan, I get a bit more into the underlying issues in this older post, which delves into terminology and how the Nazi's use of the term essentially created a very different impression of what the term meant as a whole despite it really being an intentional soft-peddling of what the camps were actually for compared to earlier, contemporary, and later examples.

If you want further reading, I would suggest Wachsmann's KL: A History of the Nazi Concentration Camp for a focus on the Nazi camps specifically, as well as Andrea Pitzer's One Long Night: A Global History of Concentration Camps which, as the title implies, is a much wider look at the concept as a whole. On the sub, I'd also note that /u/khosikulu has wrotten on the Boer War camps here