Yes....Disability benefits explain it.
I’d thought of SSI, but I think the person has to be recertified every 3 (+/-) years to continue to receive the benefit. So at most he probably had 3 years worth of checks, and that would coincide with the 3 years they write that he was homeless. Someone probably applied for or helped him get the application done, he went off to his park bench, and maybe never even knew he’d been found eligible.