I actually logged back in to answer this. any way yes peoples eye do dilate when they see something they are attracted too, ie another person or a teenager to a playboy magazine cover. lighting condition also affects dilation too much light the pupils shrink to little they dilate to let more in. I would not say this guy does not like you based on one experience you have to see it a couple of times.
Guys, you can't pick up on the pupils dilating there are too many other factors
1. Light changing in the room, yes the purpose of pupils is to control the amount of light going into the eye NOT TO TELL YOU IF THE PERSON LIKES YOU
2. The difference in pupil size is so small you'd have a very hard time picking it up without an accurate instrument to measure the dilation. We're talking about differences in mm of length
***This whole eye dilation thing has been printed in so many magazines that people have begun to believe it, and although it maybe true, what I'm saying it's almost impossible to measure it unless you are in controlled settings with the proper instruments.