I am pretty sure he is just a mix, but very striking. Is his breast brown and white or black and white?
Interestingly though, look up Brown Mottled Leghorn. Go to this link and scroll down until you start seeing them, there are a couple of pictures of them. I am not saying this is what he is, but dang, it is close.
Oh yes! Their "Ameraucanas" are mixed breed birds, who can look like anything, and sometimes their "purebreds" can have other things in them. I've had "Brahmas" that are Sussex cross, I've seen Polish that are crossed with EE, and I've seen plenty Wyandottes with single combs. Oh and of course, their Houdans are often Ancona x Polish.
This guy has too much comb and waddle to be EE though.