Any senior dev at these organizations should know to some degree how LLMs work and in my opinion would to some degree, as a self protection mechanism, default to ambiguous vague comments like this. Some of the mentality is “if I have to look at it and solve it why don’t I go ahead and do it anyways vs having you do it” effort choices they’d do regardless of what is producing the PR. I think other parts of it is “why would I train my replacement, there’s no advantage for me here.”
Realistically, the issues occurring here are intern-level mistakes where you can take the time to train them, because expectations are low and they're usually not working on production-level software. In a FT position the stakes are higher so things like this get evaluated during the interview. If this were a real person, they wouldn't have gotten an offer at Microsoft.