I'm pretty confident it's just luck of the draw. At both companies, giving interviews is an expectation for promotion, so many interviewers don't particularly want to be there and some are bad at hiding that fact.
Yeah, there is always a subjective factor involved in these interviews. You are just screwed if you meet an interviewer that doesn't like you personally for some reason and acts hostile.
Or maybe they are putting on an act to seem hostile to push your buttons.
Or maybe they are putting on an act to seem hostile to push your buttons.