I dunno about 10x engineers, but there definitely tends to be a person who knows everything on many teams. I noticed over time that if I need to ask a random question about project A, I always ping the same 1-2 people from team A for most As... then I feel bad that I'm always bothering them, start asking someone else, get vague/incorrect/lazy answers, and go back to the same person anyway ;)

I don't think it is always a senior person though... it's often a junior engineer who's been there a while.