I think it's inappropriate no matter what the race. I hate people touching my hair without permission and believe me I get it from white, black, and others. Keep in mind a lot of black women have had relaxers as long as they can remember. They typically only see natural hair that is either braided, loced, super short or pressed. But it's not just the relaxed heads who touch. This past weekend a black woman with locs was asking telling me how she liked my hair and the next thing I knew her fingers were in it.
As for this exhibit, it kinds of rubs me wrong like a black people petting zoo or circus freak show. But obviously these models are willing participants so it's their business. I have never felt the urge to touch anyone's hair so I don't understand all this. I do think you should ask yourself how you would feel about an exhibit to "touch white people really bad sunburn skin" so that those of us who have natural pigment protection would like to know what it feels like. Or "touch Asian people's eyes" ect.
If you really want to touch your friends' hair you should just ask them.