Could've been a couple of things but I think the most likely thing is that she was playing hard to get and didn't want to look like a slut in front of her friends.
You should've opened the group and engaged the whole group first, then after that told them to move over a bit.
Alternatively, you could've told her to come to the bar with you or asked the girls why they aren't dancing and head towards the dancefloor...
As for the reply, don't be bitter. You don't want to be a pissy little boy about it, you want to show her that you're independent and can do your own thing
"Yeah, I felt like missioning and found some friends on the dancefloor"
"Yeah, you lost me
""Got caught up in a game at the bar"
You get the idea...