That's my point. People aren't nearly as good at reading body language as they think they are. Sometimes they see what they want to see, sometimes they just completely misinterpret the interactions. I'm an amateur photographer and I posted a photo once of a woman who was showing off a trained owl. The photo captured her with a serious expression on her face as she thought out her answer to a question. One of the people who saw the photo immediately assumed she was angry about something.
I watched the live stream of the Avatar presentation and thought everyone sounded enthusiastic. Someone watched it and though Cameron was disinterested. Another person watched it and though Rohde was unhappy.
Who is right? No way to know. It's certainly not proof of anything.
The reports I've read about Rohde's interactions with people while sitting in the Avatar exhibit suggest he was pretty enthusiastic though, and I think that's a stronger guide, because people are much better at assessing face to face interactions.