Mixed with mutt is an interesting term? And yeah he does look a little fuzzy and ears seem a little small?
He's a good looking guy did you see either of the parents?
Mutt simply means mixed breed when you have no idea, When you know what he is you can use mutt or identify him as a GSD/whatever. That's what the "Breeder" should have done.
In any case he's a handsome boy and nobody's going to poke fun at you!
And I'm certainly not the last word Mastiffs Boxers Pitts are my background GSD's,at 7 years now are new to me.