He owns his own business and is doing this by choice. They don't go into numbers, but the fact that the article is titled "The Affluent Homeless" makes me think he's not struggling. The guy is atypical, but the people saying he's a socialist or he's being crushed by capitalism are reading their own politics into this.
My guess is that he's doing an extreme version of Lean FIRE. I know a few folks doing less extreme versions. They own little, don't go out much, and save every dime to retire as early as possible.
At least one person I know who did it retired in his mid 30s, then came out of retirement when his investments crashed at the beginning of the 2020 lockdowns. His skills were out of date so he started making way less than he was making when he retired.
The extreme run to retire early is so odd to me. Not that I think you should work until you die, but like... go out and do things while you're young, even if you have to retire at 68 or whatever. Use some of that money to live your life. What if you do nothing but work and then die in a car accident at 29?