I do suspect that's because it's the only org in that geographic area which basically concentrates the activity of members who are local to that area to that one org. I'd wager if you looked into post history you'd find of that same group of members that a fraction of them frequent the SM area, because of vicinity to Emeryville. Looking out to SJ area, I'd expect to see an even smaller number of folks from that same group. Basically they would be concentrated in the Emeryville area mostly though because of geography. For people who live over there, a trip to SM could be round trip an additional hour, and SJ an additional 2 hours out of their day on top of the travel time to Emeryville if they're coming from up north.
For example, I mostly frequent the SM orgs because it is convenient for me. If there was only one org in SM, I would basically only post about that one org. I understand that might look suspicious, but I wouldn't say that should be the only criteria for questioning the authenticity of a member's posts.
Not to say something sneaky couldn't be going on. It is nice to know you all are looking out for the integrity of the info that makes it on here. I just wanted to point out a possible cause of the pattern, so that it doesn't go unfairly against the members that use that org in that area and this forum as a resource for it.