Contrary to popular belief, the dance floor is not a place to pick up girls. Just because a girl is into dancing with you doesn"t mean she wants to fuck, many/most just like dancing, being a little edgy and dangerous on the dance floor, and going home safe and sound with their girlfriends. You are only gonna bring one home if she"s a mega slut or on drugs or really drunk, and then only for 1 night and you"ll never see her again. And even then you have to battle a million different obstacles: other guys, her girlfriends watching out for her, vomiting, etc. Plus you can"t talk and build any kind of comfort or trust, so once the arousal of the night is over she won"t have anything that pulls her back to you for day 2.
Total waste of time unless you are lookin for a (really bad) 1 night stand and you can sense that the friends she are with don"t give a shit about her banging some random guy (which is also a pretty safe bet that she has herpes).
As for the case in question, the girls probably liked dancing with you.....that"s all. But you are reading too much into it because you"re a guy and therefore associate everything with sex.
When I was younger I had a neighbor who always seemed to be mowing his lawn, and we never talked but he"d always wave and smile and seemed real friendly. My mom saw a funny joke in the paper one day about mowing the lawn and decided she"d stop to show him the joke while he was mowing the lawn, just in a friendly neighborly gesture. I told her in advance "Don"t do it, he"s gonna think you"re hitting on him" which she thought was a preposterous notion. Sure enough, she gives it to him, and from there on out he"d kinda turn his head like he didn"t see us when we drove by, because he was married and didn"t wanna invite an affair or be flirting with another woman.