<human>: Hi guys,

throwaway account since I think she remebers my username.

Anyway, I met this girl, M, a week ago during a small vacation in Germany. During our time there we went out a couple of times (always with a friend of her present since she was travelling with her), always having a good time. She is super cute, and we have a lot of things in common, like both nerdish, love the same tv-shows/films, etc.

After we both went back to our hometown, I asked her out for this Saturday, but her reply was something along the lines of "ahahah no I can't, I am busy with my boyfriend this saturday, but we could do anytime you want on Sunday" .
Soooo... Wtf is happening? During our time together she never mentioned a boyfriend, and now she drops the bomb but still wants to meet me up. I guess it can't be just a friendship thing even in her eyes, since I have only known her for like a week, and we would be meeting alone.
She didn't seem that kind of girl, but I really don't know at this point.
Anyway, I won't be around for a couple of weeks, so we both agreed to meet up when I'll be back, but I don't really know what to do, but I do really want to know either she was joking(???) about having a boyfriend, or what she thinks we would be doing/what she expects from meeting up alone with me.
How can I ask her that, without showing up like an idiot/creeper/dunno what? She is i think a lot younger than me, don't know how to approach the situation.

Give me the gist of the text in a nutshell
<bot>: lonely guy,met girl in vacation, asked her out, she said yes but told me she has a boyfriend. What to do/How to clarify our situation?