He is being very emotional in the comments section over what is effectively just opinions online. Nobody in America can do anything about Hong Kong except hold beliefs. However, in the sense that beliefs can guide action in other cases, the beliefs he reveals in his arguments seem weak. He suggests that leftists always have to support self-determination, with no real mention of what that means in real world cases. Who is the subject of self-determination? Does any subject that represents itself as an agent for others who it has defined legitimately represent them, even if it is unelected by them or even unorganized (like diffuse demonstrations and activism of slogans and such)? Somebody pushed this point in the comments when they suggests Catalonia has more of a basis to claim a nation because of its history, whereas Hong Kong is just a Chinese city that was more deeply colonized by the British. I don't care for the specific argument, but the underlying point is exactly that. Can anybody anywhere just declare a national separatist movement that then must be supported by leftists?
Of course, he somewhat ironically backs away from all of this later by suggesting that actually Hong Kong doesn't even want anything so radical as a nation or anything like that, they just want to change their electoral system to be more democratic. If THIS is what is meant by self-determination, I feel like you'd be driven to concede that there are states in America which should be allowed to ban gay marriage, abortions, turn public schools into semi-religious institutions etc. because that is what the population wants. But when even a local population in America wants "bad things", leftists tend to consider it good to fight those "bad things" using the power of the federal government, or even in localities using a state government, or whatever has the overriding authority.
Of course, he just banned this person from commenting on his channel for "being racist" or something. I actually like BadEmpanada's videos on Latin American politics, but he is clearly emotionally hung up on this case. The only other argument I remember him making was saying that geopolitical strategy wasn't a good reason to disagree with the protestors in Hong Kong, but his reasoning was to disparagingly call it doing "realpolitik". I don't see how that makes the reasoning illegitimate. I'm not going to support the self-determination of something like ISIS just because I've been given a directive to never think about geopolitics or anything beyond "support self-determination", because on one hand ISIS was arguably illegitimate, and on the other they were a genuine existential threat to just about every other state in the region. Hong Kong isn't ISIS, of course, but it's also a lot less charged to me because it isn't as obviously objectionable as ISIS. I just know I find it disagreeable that American hegemony should be strengthened through a strengthened ally in one of the richest cities in China.