He asked me if I knew her?

So I was at Fridays (a restaurant) with my best friend. About 5 minutes after we sit down my ex struts in with his new gal. Cute little thing, she's 20, he's 26, and I'm 22. So my friend goes to say hi because she and him are good friends as well. Everything is going good, I'm picking out what I want to drink when my friend comes back. I see his date get up and go to the bathroom. This asshole makes his way towards our table and asks how we're doing, both of us say good. He then proceeds to turn to me and ask if I knew his date (which I don't). He explains who she is and then says she was at our mutual friends house the night he and I started talking. He goes back to their table and 2 minutes later she's back. They proceed to laugh loudly and talk loudly until I finally get up to leave. I'm out the door 5 seconds flat while my friend says goodbye. Keep in mind they haven't gotten food, only drinks. As she heads out, he and his new gal follow. He proceeds to wrap his arms around her and kiss her on the fourhead.
(We had a horrible breakup 6 months ago, he was on drugs till about a month ago)
Why would he act in such a way?
He asked me if I knew her?
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