I suppose it's possible Bryan might still live with his mom when he's in the local area and not off on some production with Kevin or involved in his own projects. Reality shows always exaggerate something to try to make the participants in the program more interesting or amusing to the viewer, so I'm sure the image of Bryan hanging out at the Stash all day and then heading home at night to crash in his mom's basement is something that helps play into the theme that these four guys are grown (and in most of their cases middle aged) comic and sci-fi/horror geeks.
Remember, this show is aimed at grown comic and sci-fi/horror geeks and folks who love Kevin Smith. They want the average audience member to feel like Bryan is a lot like them.