The AI wrote code which worked, for a problem the submitter had, which had not been solved by any human for a long time, and there is limited human developer time/interest/funding available for solving it.
Dumping a mass of code (and work) onto maintainers without prior discussion is the problem[1]. If they had forked the repo, patched it themselves with that PR and used it personally, would they have a broken brain because of AI? They claim to have read the code, tested the code, they know that other people want the functionality; is wanting to share working code a "broken brain"? If the AI code didn't work - if it was slop - and they wanted the maintainers to fix it, or walk them through every step of asking the AI to fix it - that would be a huge problem, but that didn't happen.
[1] copyrightwashing and attribution is another problem but also not one that's "broken brain by the existence of AI" related.