What the hell happened?!

I was out last night and walked into the club, very shortly after some random girl bumped into our group and was into us straight away, she seemed pretty cute so I went for it. Things were going well, she seemed really interested and was being incredibly flirty, so I was thinking 'great, that's me sorted for tonight'. However, she was trying to talk to me a lot and I only managed to get a general idea of what she was saying but I just couldn't hear a word over the really loud music. I think she'd lost her friends though.

We ended up on our own though, had a few drinks, exchanged numbers and started going for it on the dancefloor. I was getting vibes off her that she was losing some interest though as her eyes started wandering around, however she grabbed my hand and held on when some random guy tried to start dancing with her. I pushed on though (as I was still getting enough indication it could happen) and when I thought it was about the right time (or at least in my head) to make a move, she went and said it: 'i've got a boyfriend'. With both of us feeling awkward we ended up parting ways there and then.

So i'm just wondering what was going on here? Does it sound like she was just playing me? Was I just being wayyy too slow and missed the boat? If she actually does have a boyfriend why the hell was she acting like it was on? Do a lot of girls do this?

I'm probably overanalyzing this but I am really confused and still am about what happened especially as she's probably the first random girl in a club i've actually came in contact with in a longgg time.