It is possible to recognise the creativity his opportunity to focus on doing his own thing has allowed him to express without intending it to downplay the challenges of his mental illness.
Most people with severe mental illness do not describe it as something that has freed them, nor given them focus, to pursue the one thing they really want to pursue.
There's a bunch of positive stuff about severe and enduring mental illness; and we need to protect people so that they can live the way they want to live; and we need to be careful to avoid the abuses of treatment that happened in the past (and still happen today); but romanticising a severe and enduring mental illness is fucking annoying.
This isn't his calling, it's his delusion's calling. and he's not freed from restriction - that's a fucking idiotic thing to say about someone who lives in relative poverty with severely limited options about where he lives and who with.
The near complete lack of understanding of severe mental illness, coupled with glib feel good platitudes, do real harm to many people.
I have found in my experience that the people using and applying the label 'mental illness' see it as some sort of barrier betwixt the person they are discussing and themselves. This is the 'normal' barrier. by relgating the person to this place (behind the wall as it were) a number of very large assumptions must be made, and my inclination is that some of these assumptions are pointless.
once upon a time, abstraction may have been viewed as a nasty 'mental illness'.
"Look at Grok. He so dumb. He tell me finger number could be more than hand plus hand. retard say dumbest things."
We call people who are socially inept mentally ill because they do not fit will into the structure of society, not because they are actually broken. There is a difference between Down's and Autism.
My advice though to you directly though is there is more to life than casting judgements, and when it comes to personal desires I have a hard time telling someone they are wrong if they are not infringing on anyone else.
You might do better to keep a more open mind to what drives people yourself.