You're far too free and certain with your condemnation.
I have multiple autistic, immediate family members that I would lay down my life for. I've used that word. In the right context (certainly not in the public sphere), I don't even regret it necessarily. It's not heartless. It's a word.
We live in a society that acculturates us to offensive language so that it becomes reflexive sometimes, where so much of our strong language is rooted in denigrating a group of people that it's easy to use a term without the specific malice originally intended for it. When you use language that insults another group of people directly without thinking about it, you should be rebuked. We should presume that, at best, you have insensitively chosen to ignore the way that group feels and suffers from prejudice. At worst, we should be wary of your actual malice.
When you use language that does the same thing to your own people, or to yourself, you should still be rebuked for your thoughtlessness, but I can't see imagining that you're insensitive to the pain of your own children, or that you have malice towards your own flesh and blood. It becomes a poor choice. It occupies a completely different context for me. It's something you should be reprimanded for, especially when it's in public like this, but in the sense that you're carelessly allowing other people to hear it and perhaps normalize the term where it should never be normalized. Not in the sense that you have actual cruelty in your heart.
In the end, we care about these words because of the intent reflected in them. They're not magic spells. I don't see a reason to presume his ill intent towards the mentally disabled anymore when I know he has a child with issues. He was careless, not cruel, and he apologized appropriately. That's it for me.