Autistic children are children, the same full irritating, exhuberant, noisy and magnet for troubles in a small package than before, but with a plus of cleverness, strange ways to do things, uncommon hobbies and extravaganza. The idea that an ill children tired and with less energy than usual would behave better is not a total surprise.
They say when having fever, the mice communicate with peers better. When children are under the weather, they don't seem to communicate better.
My daughter, every time she has a cold, which since daycare is almost always.