I've experienced something similar yet different as a contributor.

I've received comments on MRs I had created from random people (not maintainers) that were just AI generated suggestions on how to improve the changes that came from seeing the changes, without actually understanding the issue and its context.

I'm not really sure about what the person was after, there was no clear incentive.

Apart from that, at my day job, I had to deal with colleagues submitting absolute trash AI generated MRs, with emojis in the comments, imports in the middle of the file, and placeholders. Luckily you can also do the first round of QA using an LLM and ask it to detect potentially AI generated leftovers. Low effort contribution -> low effort QA.