I wonder what you would do in this situation?

Our local library has a child's storytime one night a week, and we've been bringing our 7 year old son. Last night I was a little embarrassed when the art project included drawing a dog, and he made a point of saying loudly "this dog is peeing" and clearly showed the dog peeing. Then, a little later, "this is the dog's penis, he's peeing out of it", then he added a fairly good representation (he's a pretty good artist).

I didn't make a big deal out of it, I did ask him to be a little more quiet. One of the mothers (I've known her for several years), leaned over and jokingly said "that art is known as 'realism'".

So, what would you do? Would you say anything at the time? How about afterward? My son seems to crave attention in a crowd.

Should I even give this a second thought?