I had a rather bizarre experience this weekend. Bunch of relative strangers; we were all doing a training course together - went out for drinks after the first day of training. Few drinks down range and two or three of the, oh, about 10 people around the table, start talking about board games and D&D. It was just such a change from what I was used to. I can honestly say I don't recall anyone just bringing up gaming in a group of strangers like that.
So, yeah, I can see why they might call gaming - mainstream.