^ Well, on her part it just wasn't a very smart thing to say. She had no way of knowing, but if someone is sitting down, its best to assume there is some reason for it.
Also, handicapped or not, there are people who enjoy concerts in a different way.
Anyways, it would have been better to think before speaking a bit in this case.
I'm sure afterwards Ayu was probably like "man, why'd I have to go and say that?"