I can't read Jon's mind so I don't know why he liked it. I don't know whether he agrees with it wholeheartedly or only partially, or whether he liked it to bookmark it or even if it was an accident. It seems like the tweet was decrying the political manipulation of demographics rather than the fact that demographics are changing. I think it's a bit of a stretch to call that White Nationalism regardless of whether you or I agree with it. What I do know is that Jon does not put his politics in his videos, he has in the past many times expressed anti-racist sentiments, and frequently engages with the groups of people that White Nationalists would not.