O.k I am super confused here (best answer 10 points)?

O.k so yesterday I asked this girl im friends with if she has a thing with a guy I saw hitting on her in class (I was just curious) she reply-ed with *its none of your business that we had a thing* then she sent me another text right after saying *no we don't have a thing* and then I told her I was sorry if I bothered her with this question and it ended with that, then when school ended her friend came up to me and told me she was all weirded out by it, so I text her to make sure if it was true or not and ya she was weirded out by it, and I am all confused by this like how was me asking if she had a thing with a guy sound weird and like what did I do wrong I didn't know asking a person if that have a thing with a person was coincided a weird or creepy thing to ask.... help guys?