I would classify being able to live at his office without being tossed out into the streets, and being given a home after that got to be too much for the school, as living off his celebrity. The "technically" in "technically homeless" is a major difference between what Stallman has to deal with vs what non famous computer scientists/software engineers have to deal with.

I understand he's forgone the amount of wealth he could have accumulated by just working in the software industry in the name of his cause, and that is laudable. However he thinks everyone should do this despite the greater burden they'd have to shoulder. All the people he tells shouldn't be making non free software so they can support themselves and their families are not going to be given free lodging by MIT.