> I was like, "You know when you do new[] you need to use delete[]?" as all of his deletions were without [].

This seems like a pretty major lack of a specific piece of knowledge on the senior developers part, yes, but it seems like a much more unforgivable miss on the part of the code reviewers. Was the team stuck in a rut where only a single person (with coincidentally the same blind spot) was reviewing his code, or did multiple reviewers somehow miss this?