Similar to how graduating college shows you were able to work hard and learn many different subjects effectively for four years, being able to solve a google problem shows that you A) are smart enough to have understood and retained it from when you were first taught it or B) were driven enough to sit down and learn tough conceptual problems in a few weeks.
So, its less that you know that particular subject, and more what you being able to pick it up is an indicator of.
My point is that most of the very best front-end developers I've met don't have CS degrees. So it seems unfair to penalize them for something they've never been exposed too. There are other ways to assess someones conceptual ability.
So, its less that you know that particular subject, and more what you being able to pick it up is an indicator of.