All it tells us is that at least some competent people make it through their interview process, but it's a rare company that has an interview process that effectively filters out all competent people and remains a going concern for any length of time.

The fact that Google produces "pretty decent" products doesn't actually tell us whether their famously stringent comp sci trivia quiz system produces any better results than, say, throwing a packet of resumes down the stairs and hiring the ones that land face up.