Niceness = Flirting?

For the record, I don't think I'm good at flirting.  Quite frankly, I think I'm really bad at it.

That being said, there must be something in my mannerisms that makes people think I'm more interested in them than I actually am.  It's not physical as I'm not really a touchy person.  And I don't play with my hair or do any other flirty indicators in normal conversation.

I'm left to conclude that me being a nice person make guys think that I'm soo into them. Can't a guy and a girl have a normal conversation without some sort of pretext?

I was at a pub once where Guy A told me to hit Guy B.  When I asked why, he wouldn't tell me, so I kissed Guy B on the cheek.  Guy A thought this was funny so he struck up a conversation with me.  We talked about me being fairly passivist, but mostly I was thinking of a way I could end the conversation. When I "heard" one of my friends calling me, he continued to follow me and ask me for my number.  After a bunch of "I'm sorry, but no"'s, I flat out told him I wasn't interested.

Do guys feel that if a girl takes time to talk to you, she must be interested?  Can't I just be bored and am looking for some way to entertain myself?

It's not just men, either.  I met some friends of friends, let call them Ross and Rachel.  We chatted for a while and went about our evening.  Later, I find out that Rachel didn't like me because she thought I was flirting with Ross, who in truth, I thought was arrogant and annoying.  They later broke up and Rachel and I hang out sometimes.  She still gets jealous if I stand too close to the guy that she now likes, but at least I'm prepared.