Dunno. Up ears, long body, short legs, black coloration (with a splash of white). I’d say he was a black German shepherd mix, but the face looks more Lab-like to me.
Edit: Buster’s dad checked in below, almost two years after I first ran into Buster, and filled me in on his name. And the more I look at Buster the more I think maybe black German shepherd, not lab. Those ears, man. Those ears.