You don't have enough info to decide. A scientist mixes two chemicals and gets a reaction that's different from the one he was expecting. Does he decide if it was good or bad? No. He moves on to find out why it happened, without attaching any emotional meaning to it.

My guess is she's sad and you made her laugh, and then she had to go back to reality. Maybe she thinks she's going to fail for the test she just spent ages cramming in the library for.

The issue here for us to discuss is that you're too outcome dependent and worrying too much about what happens.