This is outside the scope of this thread, but...frankly, people pay lipservice to inclusion. People with autism and SM often cannot (can not, not "will not") initiate communication. It's too much work for people to accommodate. They think SM is just not speaking, when it's often a communication inhibition, and that includes initiation of communication in all forms including writing. So he could respond to an email, but not send one out.
No he could not let anyone know it was not personal - he would need someone else to do it on his behalf. If someone asked him if it was personal he might be able to reply that it isn't.
There's still a basic assumption in your post that if he could just find a way to .... - well he can't. That's the disability. Just like if he couldn't see at all it wouldn't matter how much he screws up his eyes. And it doesn't matter that some people with visual impairment can see shades of light. He can't see at all.
What he would need to work is a totally non judgemental employer who would give him a year, during which they anticipate that he will be unable to initiate any communication. They would have to check in with him, because he can't check in with them. If they could do it for 6 months, they'd maybe begin to get some speech. After a year they would find out he is very funny, very witty, extremely clever and knowledgeable. But no one puts in that amount of support, so as far as I can see he will never work.
I appreciate this isn't the situation in the OP. But maybe you can see why I find assumptions of ill intent -with very little evidence - when communication is concerned extremely triggering.