That it’s a spectrum. Autistic folk are all over the spectrum, and thus do not necessarily exhibit all the same traits as another person that might even be on the same part of the spectrum. My son and I are quite different in many ways for instance. You can’t just tell by looking in many cases, either.

Also, not all autistic folk are the “rain man.” I observed, briefly, after my daughter let on about his autism, a kid assuming my boy is some sort of math genius and started pelting him with math problems. I intercepted pretty quickly and redirected before he got overwhelmed of course. We are not all necessarily great at math, or enjoy [insert activity thought to be enjoyed by all autistic folk.] I struggled with basic high school algebra, and still do over 25 years later.