This practice seems common. I've had recruiters at several top tech companies (including two of the FAANGs) tell me this during initial chats.

I imagine recruiters actively want you to succeed and get hired because that benefits them too, so they do what they can to aid you in your chances. They'll tell you the official, pre-canned lines about "we're interested in what your thought processes are and how you think", but then they'll also tell you the truth and recommend you take some time to grind leetcode.