What they are seeing is the result of years of therapy, teaching children how to function. With varying degrees of success.
It doesn't mean they no longer have autism. It means that certain behaviours have been successfully modified.
My eldest used to smear his poo over his face. He doesn't do it any longer. We've managed to teach him that is not acceptable.
Doesn't mean he's any less autistic!
My youngest talks now, instead of just repeating "clifford the big red dog and tasty food now at mcdonalds" 18 thousand times a bloody day.
Still autistic.
My children (like all our children on the spectrum!) have to have many many many MANY hours of work to teach them things that NT children pick up without even trying. Now they have many of those skills it doesn't mean they are less autistic! The level of input required was MASSIVE. because of their autism. The maintenance required in order to ensure that they keep these skills is huge. You're constantly pulling them back to you.
But then you get someone coming along, looking at a child as a toddler and looking at them 10 years later and saying wow, they're doing really well, they're cured. No. They're not cured. They're coping.