The guy I used to be with had very particular sexual interests and wants that resembled those of a Daddy Dom. However, he refused being interested in BDSM. To him, he just believed that relationships worked better when women are submissive to their men.
There are many ways BDSM is practiced, maybe your boss has misconceptions. Maybe he's worried you are going to take him somewhere where everyone is in tight, shiny leather and chains. I think the best thing to do is just to talk to him about it. Tell him that you want to go be social (and open about your sexuality) somewhere where the people don't look strangely at you for your sexual interests.
He should at least try it, if you guys go somewhere and he feels uncomfortable/out of place you two can always leave.