I would second the Asperger's question.

I'm not sure why people are saying here that you seem to be against frogs. You said it was endearing until he was blowing stuff off with misleading explanations to do frog stuff. I'm disappointed with how most of these comments minimize the fact that he misrepresented what he was doing when you invited him to a function that strengthens the social ties that bind people in future-oriented relationships together.

However, if this is an Asperger's/ASD thing, this could explain why he doesn't see the big deal. He would not necessarily see the broader importance of the things he's opting to miss, other than being something his girlfriend suggested, and he could be SO zoned-in to his hobby that he doesn't think of it as misleading to describe it as work, even though most people would recognize that as a b

If it's an Asperger's thing and he's not already diagnosed, you'll have to think about how to bring up the suggestion and it could be a long process of learning how to take his perspective and show him yours. However, in general, on your end it will involve stating social expectations and the degree of importance you assign to various behaviors or events more explicitly. It might help for both of you if he made frogs a part of his actual work, e.g., go to grad school and study frogs.

Otherwise, you need to insist on honesty. If he intentionally deceived you so he could get out of the dinner and do whatever, that's a red flag; if he won't stop doing it, that's a flaming red flag. If, when he's honest, he doesn't care enough about the things you want him to do to support the relationship relative to his hobby and you can't find an agreeable compromise, then that's a compatibility issue.