That's not what the term "strawman" means. What you mean is it's an excuse used to oppress people, and that may be true but you'd have to give supporting cases. (Certainly it has been the case for LGBTQ people being oppressed in the past, even currently in some countries.)
Mental illness is also a real thing and a real problem, and people with serious problems who need medication often live outside the bounds of normal society. But that issue is not going to be solved here, and I think it's a distraction from the actual topic because the reality is he was on other people's property where he wasn't welcome.
I think they're describing your applying a mental disorder to someone when there's no evidence of that anywhere in the article-to justify your position against the comment you responded to-as being a strawman.
Mental illness is also a real thing and a real problem, and people with serious problems who need medication often live outside the bounds of normal society. But that issue is not going to be solved here, and I think it's a distraction from the actual topic because the reality is he was on other people's property where he wasn't welcome.