You're absolutely right. You don't have a crush just because you were on a blind date with her. That would imply that you'd have to have one because you went on a blind date with her.
[And he wasn't being sarcastic, either.]
But the fact remains that I've seen it multiple times since then. Once or twice is a fluke. I'm pretty certain you're crushing on her. It may not be a huge crush, but it's definitely a crush.
[Action]
You're absolutely right. You don't have a crush just because you were on a blind date with her. That would imply that you'd have to have one because you went on a blind date with her.
[And he wasn't being sarcastic, either.]
But the fact remains that I've seen it multiple times since then. Once or twice is a fluke. I'm pretty certain you're crushing on her. It may not be a huge crush, but it's definitely a crush.
And that's nothing to get upset about.