Why did this guy go from super interested to completely uninterested?

So I recently met this guy through a mutual friend, and he is very sociable/flirtacious. We started talking, and it became clear that he was very interested in me (physically, that is)... he essentially invited me over to his place to hook up, and we established a sort of friends with benefits dynamic. We never got around to actually hooking up (due to random circumstances), but he always persisted and made it clear that he was still down. I was texting him one day and was rather flirty/suggestive, but he wasn't reciprocating any of it. I asked him if it was a bad time, and he said he was just overwhelmed/stressed out with work (we're both freshmen in college). The next day, the same thing happened. So I said I understood, and backed off for a few days. Later that week, I said I would be at a small show his band was playing at (and hinted that we could "hang out" afterward), and he said he just didn't have much of a sex drive at the moment. Flash forward to the night before the concert, and he's telling me that he just wants to enjoy the other bands playing and that he has a lot to do at the show before his own band goes on. He said that concerts are a bad time because he's always busy, which honestly didn't add up because in the past he's suggested we hang out at a show. I said I understood and it became clear he was definitely no longer interested. At the concert, however, I didn't even see him in the crowd (even though he said he wanted to enjoy the other acts), and he definitely wasn't "busy" because he was just hanging out with his friends outside the whole time.
I'm honestly so confused why he went from very interested/persistent to suddenly lying to me and coming up with many excuses just to avoid hooking up? Only two weeks prior he was coming off really, really strong...
I know this seems very trivial but I'm new to this whole casual/hooking up dynamic... so I guess I can't tell if this is normal or not, or if it's because of something I
Why did this guy go from super interested to completely uninterested?
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