So I just got linked to this https://e621.net/posts/5434174 and it has the tags AI_assisted and I was under the impression that AI generated art wasn't allowed on the site? It'd suck if this was allowed because the site is just gonna get flooded with that crap

No. Don't stir up drama over nothing.
https://e621.net/help/uploading_guidelines

• AI Generated content: No AI generated, or AI assisted artwork.
• Exceptions are currently for backgrounds (treated like using a photo as a background, quality rules apply); for artwork that references, but does not directly use, AI generated content; and for audio in WebM posts.

Plus, the ai_assisted tag on that post is a result of someone's beef with the artist, it seems.
Their long meltdown over it got removed, and they received a record for it.