Only guessing here but I think it most likely due to eye contact. Both species see something in the other. I know I've seen it many times with marine mammals and the larger, smarter fish when diving. Grouper and wolf fish literally look into your eyes when checking you out.
Other objects usually don't get thrust into their faces like cameras do.
I’ve never had a chameleon get upset at a camera or a cell phone. I’ve had some that seem to pose for the camera. I do interact with my chameleons everyday and make allot of pictures so that probably makes a difference,
Yeah, like anything it's what they're used to and comfortable with. If you brought any "foreign" object near him/her she'd be spooked. Sometimes you have to really try hard to think like a chameleon and not a human, haha.