Many companies do a pre-interview screen performed by recruiters to filter obviously bad candidates. I have personally helped construct such screens -- though not at google.

Ensuring the recruiter understands the difference between an answer over their head and a wrong answer is crucial. What we did was to make sure the recruiters understood that answers they didn't understand needed to be surfaced to someone in engineering for a sanity check.

Often our strongest candidates would give an answer which recruiting wasn't capable of vetting. The key is making everyone aware that the answers may not fit the script, and that this is OK. Recruiters shouldn't be judging the technical details of an answer; they should be looking for "gosh I don't know I've never seen that."

Pre-screening is sadly necessary when doing high volume recruiting. There are a LOT of people out there who grossly inflate their competency.