That was my take really. I didn't think he laughed because if brought him the joy we feel when we laugh.
The thought that he learned that it's a happy sound and he's repeating it because he's happy makes a lot more sense. It's easy to try to anthropomorphize our birds but they really aren't people.
Either way, it was proof to me that he needs more outings like that. Thursday will be a quiet day at work so he's going to come with me. I live close enough that taking him home if he gets overwhelmed won't be a problem. I'll keep you posted!