[_greim_]

I believe the mindset behind this behavior is A) they take it for granted that you're proficient in your stated area of expertise, B) they're not necessarily proficient in your area of expertise, so wouldn't be able to assess your skills anyway, C) algorithm knowledge is hard to fake, so your false positive rate for hardcore engineers will be low, even if your false negative rate will be ridiculously high.

Google's publicly available prep material reinforces this third point, even if they don't say it explicitly. They recommend books, point you toward places where you can learn the concepts, and tell you if you fail once, try again in a few months.