IIRC in Steven Levy's book Hackers, published in 1984, he is described as renting a room in the house of a dentist or retired dentist.

I always thought the "squatter" description referred to his spending much of his time at MIT and keeping things at MIT without being employed by MIT. (Stallman quit his MIT job when he started GNU out of a worry that if he kept it then MIT might claim ownership of GNU; the legal ramification of the GPL weren't understood as well back then as they are today.) I don't think his use of the word implies that he had nowhere else to live.

I searched the page you linked for "home", "squatter", "vote" and "register" without finding any text the supports anything in your comment. I hope I don't come across as antagonistic to you; I am sincerely curious whether Stallman was ever homeless (i.e., ever lacked reliable access to private indoor space with a door that could be locked).