As far as I understand Lisa and Ted told him about how they only met based on Brokie forums and tried to explain a little bit about how the Brokie community functions. So, even if Jake himself doesn't look at these websites (which it sounds like he really doesn't based on their report about the conversation at lunch) he at least has some idea about them.
LOL, so here's a question for folks... if for some incredible/ hypothetical reason you had a chance to actually show Jake BetterMost (say you bumped into him at a coffeeshop while you had BetterMost up on your laptop), would you do it?
I would expect that if he actually saw BetterMost and all the posts and even a thread like JJJ, he might indeed be a little overwhelmed (let alone seeing DC and EJ in addition to BetterMost).