I agree, but the story he tells is quite different. And just because you can call up the anger and fear of a situation for a role, does not mean you are suffering from PTSD. It means you are a good actor.
None of his actions in later years showed any fear of flying, or getting back in the saddle, that any kind of PTSD would have shown.
There is men who have PTSD but refuse to be crippled by it. I think Stewart was such a man.