This despite that my best known essay is titled "Object Oriented Programming Is An Expensive Disaster Which Must End" a fact the interviewer should know if they'd looked at my resume or spent 10 seconds looking up my name on Google. Wikipedia now lists me as one of the critics of OOP -- https://en.wikipedia.org/wiki/Object-oriented_programming
I'm lucky in that my position is comfortable, so I can laugh off stuff like that, and either educate the person I'm talking to, or end things quickly by explaining that there is probably some kind of cultural mismatch.
But it shows a remarkable laziness on the part of the people who, in theory, want to learn more about me.
The question is, can you whiteboard? They will be testing that. If you can, then all is golden and you probably didn't need to waste those 4-6 years getting that PhD because what you will be working on will have nothing to do with your topic of research (unless it was AI/ML).
If you can demonstrate that you understand programming concepts and can learn, then it's not much more to assume you can write code. If you need someone who can hit the ground running with some specific technology, then you might need to go deep into it, but not to find out if someone can program.
I think you're overthinking the feedback you got.
If it was at one of the big names, they have the luxury of being picky. They can't hire every qualified candidate, so they have to reject most of them. As the interviewer, the company policy likely dictates the interviewer give a reason. Which puts the interviewer in a bind because it implies that there was a good reason for rejecting you. So they'll put canned statements like what you got.
I recently got rejected. And one of the reasons given was something that 3 of the 5 interviewers had explicitly told me they don't care about. I recognized it for what it was - they feel obligated to give some reason, so they nitpick after the fact even though they told you they were not going to nitpick.