It also uses a cloud fingerprint database apparently according to the second paragraph:

If you turn on “Show search button on lock screen”, each time you tap to search Google receives a short, digital audio fingerprint to identify what’s playing.

Is this for posts that mods haven’t manually approved, or is it completely random which posts have not been ‘reviewed’? I swear I’ve seen this on posts with thousands of upvotes that surely must have been approved by then…