Autism is a major disease. I am not sure why you would want anyone to call you that. I would much rather call someone by a name then a disease. As I find calling someone by a disease to be derogatory. I also find it heart
OP can identify with whatever makes him/her happy. And major disease or not, you're giving it a negative connotation when there shouldn't be. Autism just means your brain is wired differently, and there's nothing wrong with identifying it. You essentially just shamed him/her, and as the mother of two children on the spectrum, I'm both saddened by your response and hopeful the the OP knows they've done nothing wrong.
Less judgment in the 'World is something we all appreciate.