I’m not from USA, black, nor a native English speaker, but due to Linguistics I can give you guys some further info.
AAE (Afro-American English), in a nutshell, is a group of English varieties used by some speakers from USA and Canada. In a lot of aspects they resemble geographical varieties, like the ones you’d see in plenty other languages, but there’s a key difference: it isn’t used by people “of a certain region”, but rather by people “of a certain race” (black people).
This is mostly but not completely spoken (cue to the term AAVE - the “V” stands for “vernacular”); it affects also the way that those people use the written language. So often you see AAE features in written English, like:
Negative concord - for example, "I don’t want to hear nothing about this shit, man."
Habitual-be - for example, "They be talking about this everyday."
bits of non-standard spelling, due to phonetic differences
expressions and vocab typically used primarily by black people
What the article is saying is that LLMs are biased against those features. It’s a rather strong bias, and not noticed for a geographical variety used as reference (Appalachian English). In other words: the LLM has been fed racist babble, and now it’s regurgitating it.