I personally would try not to use the word 'naughty', it has really negative connotations especially when they arent being 'naughty' in the true sense of the word.

Ive been trying to figure out how to deal with this myself, since Ds2 (who has autism) is starting school next year which Im sure will bring up similar questions from his classmates and also because DS1 (6.5) has started noticing things. I think that explaining that everyone is unique and sometimes people's brains work differently to others, especially in the case of people with autism, is a good start. Maybe explain that sometimes this means there are things like noises or touches that make them sad and you can do xyz to help them out and make them feel better. The social cue/emotional understanding issues would probably be good to mention as well. Maybe say that sometimes that people with autism dont understand facial expressions or things people say when they are feeling happy/sad/angry etc and that its ok if they dont understand, it doesnt mean they dont care. We tell our Ds1 that Ds2 sometimes needs to have his personal space respected alot more than other people, that when he is scared or angry or happy it takes him longer to process it and touching him or entering his personal space makes him scared; and that when he is scared sometimes he acts out by hitting or making loud noises.

You will be surprised at just how accepting, patient and accommodating kids can be. Much more so than adults I feel.