He wasn’t in his home, he was outside where people—neighbors, employees, the mailman—are able to view him, which is his motive for doing it in the first place. Do you walk around your yard without any clothes on? If I were your neighbor and saw you I’d think you were a pervert.
Joe is a pervert, but compared to other things he does, this is small potatoes.
The article implies that the skinny-dipping was in the privacy of his home, maybe in a backyard surrounded by fences, hedges. (And, no, I would never do that. I'm much too shy.)
JFK used to swim in the nude in the White House pool.