Sounds like a guy I knew in the Marines, long ago.
He was so hairy, he could walk down the street naked and people would think he was wearing a gorilla or Big Foot costume...................
I got a couple bro-in-laws like that.
Iām not that hairy! LOL. Also black hair.
Apparently when you have XYY you have double the androgen receptors in muscle, various bones, and, yes, hair.
So whatever androgens (eg testosterone) floating around had almost 2X effect. I easily could have been a bodybuilder, although that would require a lot of shaving.