Am I Being Paranoid?

So my girlfriend and I have been together for almost a year. Early on in our relationship, I came over to her apartment and there was a guy standing outside waiting for her to answer, and he looked at me confused, stating that he'd come over to see if he could borrow some sugar. He was a bit intoxicated, and he was at his friends apartment which is diagonal to ours--we can see their balcony and they were having a party (as they always do) it's sort of a party apartment. In any case, I thought it was sort of odd, and it kind of bothered me at the time because it was so random. A few months later, we now live together. The thing that had me sort of questioning things is that the outspoken neighbor, who's always drunk, has referenced this 3-4 times over the past several months, screaming, "Hey I want to see if I can borrow some sugar!" to her when she's on the balcony by herself. Keep in mind, he's referencing the friend who came over to borrow sugar a long time ago. To me I don't understand whats so funny about the reference that he'd need to keep bringing it up unless it was something fishy.

She maintains she'd never met the guy until he showed up at her apt randomly that night. There are a couple of other odd things I'd noticed earlier on in the relationship. For example there is another guy who'd come over to use her scale, which I also found weird. I guess he'd come over a couple of times to use it when I wasn't there, but also came over to use it when I was there, because he doesn't have one. He'd also asked to use her printer when I wasn't there. We live in sort of a party, outgoing huge apt complex community, so random stuff isn't out of the ordinary.

I haven't noticed anything recently that's strange but have always held stuff like this in the back of my head. Am I nuts/paranoid, or is there something here?