I've been in a ton of debriefs at this point. I no longer feel bad about any rejection I've had from any big company. "Dice roll" is a perfect way to describe it. The number of things that someone will raise an arbitrary red flag over is endless and largely down to personal bias / mood of the interviewer.

I've seen people discredited for not setting up some large inheritance hierarchy for their whiteboard design question. What's "Doing it Right" for one person (me: avoid inheritance like the plague), is someone else's "this guy couldn't code his way out of a paper bag".