There are lots of dialects and sociolects in English - or in most other languages - that most non-linguists refuse to consider as separate languages. The fact that many of those language variations lack prestige, and are associated with certain groups, doesn't help of course, but that's not the main reason. The main reason is that people (including the actual speakers of AAE and the others) have political, ideological and practical reasons for viewing AAE and other dialects/sociolects as variations of English and not separate languages, because if they were as willing as linguists to see them as different languages, the variations would grow further apart and at some point in the future there might not be a common Standard English anymore. A situation somewhat along those lines exists with Flemish and "standard" Dutch, with the various kinds of Arabic, and I'm sure many other language situations.

So while MightyYT's way of phrasing it was somewhat offensive, I think you're exaggerating by accusing him of racism just because he doesn't think AAE is a separate language - I'm guessing it's part of a general attitude he takes towards all kinds of dialects and sociolects, without race playing any particular role.