We can not say for sure since we didn't experience your experience first hand.
Nevertheless what the other posters said were very relevent.
I may add another point that can also be pretty common: conscious or subconscious attention wh*ring.
I also had my share of high interest that turned out to be total disastrous failures. But now looking back, it's pretty clear that they were NOT genuine high interest, just attempts to get my attention.
One little example:
Sometime back I joined a campus musical, I was the best male dancer on the team. Since the first day, one cute blond girl was eyeing me real bad. And starting from the second time we rehearsed, she asked me to come to her dorm room to listen to the other songs we would be playing for the show. It was so unbelievable that she actually did that in front of a few other members of the crew. Ok nothing happened that day, but I was so sure that things were already "in the pocket" as the French would put it.
Of course it was too good to be true. One month later, I learned that the whole time she had a boyfriend, and most other girls on the crew knew it. I learned that because one day she couldn't make it for our rehearsal (she was actually the dance leader of the musical) because her boyfriend left her very weirdly for no reason, and she was crying her heart out that she couldn't do the rehearsal. And she called me to cancel the rehearsal.
After that relationship between us was almost ice cold.
Anyway, to sum things up, as the Chinese would say: love doesn't come out of nowhere, neither does hate. If some girl shows "high interest" out of nowhere without even knowing you, something's not right.
From my personal experience, genuine high interest doesn't build up instantly, it takes some time (it might be just days, but definitely not instantly). And girls with genuine high interest are real nervous in front of you. You will catch them checking you out, but at the same time trying not to. They will talk to you, but many times it feels they don't know what to say, etc etc...