The post did not make any positive encouragement, make a case for mental health, or even make a suggestion. It came in as an accusation that anyone who chooses to live that way is abnormal. By definition it was a microaggression, so triggered people are reflex responding.
Frankly I think that if you feel called out by this post it has more to do with you than the original poster. "How do people not go crazy if they're stuck inside too long" is not a novel sentiment.
I can agree with you about this specific post (without knowing the tone of the question, it could be earnest rather than insulting), but I've always found the "touch grass" saying to be condescending af.