The claim was "constantly recording every conversation within its field of reach", not if commands after "OK Google" are send to Google servers. For the commands Google's terms-of-service allow (themselves) to use data to improve any of their products and that includes personalization (advertising), so I doubt such a firewall exists.

mtmail already composed a better answer than I am capable was, and has pointed out that what you ask was not the question I replied to. Your question, though valid, might have been better asked as a top-level question. Your other top-level comment implies a position that you’ve already taken (and hence the downvotes for that post). Asked as “can some clarify whether or not...” rather “I assume bad things about Google, it’s up to you other folks to dispute it...” can go a long away toward getting a useful answer and reducing downvotes (thereby reducing your chances of an answer).