could be any of a number of reasons (or combination thereof) why you got that job.

* comparison to other candidates * truthfulness/honesty * track record * personality

At some point, the "I know nothing about this" really isn't all that true, especially for senior dev folks. I'm not sure there's much tech I couldn't say "I know nothing about X", because I understand fundamentals. I don't know much about a lot of tech - erlang/lisp/rust all spring to mind. But I understand variables, scoping, order of operations, etc - even if the behaviour is somewhat different from what I'm used to, I know some fundamentals that I didn't know in the beginning (or... were not muscle memory on day one).