I think you went there with some (perhaps hidden or unrealized) expectation and when the evening did not materialize to your hope, you were no longer interested. And to convince yourself of your neutrality, you put a negative spin on the interactions and her appearance.
I do not even believe it was a conscious expectation, as in I hope for a, b, and c tonight. But when whatever scenario you subconsciously wished for did not play out, you shut down and removed yourself quickly from the environment.
Maybe it is a change in feeling or perception or you are trying to convince yourself you should be interested or pursue because the relationship does not seem to be shifting from its current position.
It is almost as if you want her to continue to pursue but raise the level.
It is about her not meeting your unspoken expectations.
