How do you know that?

Overheard while waiting in line for the bathroom at a family friendly (no alcohol allowed) showing of Kooza by Cirque du Soleil.
30ish woman #1: So do you know Matt*?
30ish woman #2: Yeah he is a nice guy. Sexually he is into tying up and stuff.
#1: How do you know that?

(I love San Francisco!)