It's a bunch of hogwash. An old myth that any dog with black on its tongue is part chow.

 
You are correct.
 
As Jovial found and I have found before, many breeds may have black pigmentation on their tongues. Shadow is a mix of Siberian Husky and Lab. And he has some black spots on his tongue. And no, he doesn't have an Chow that I can detect or surmise and he's been appraised by breeders/owners of Labs and Siberian Huskies and he is most definitely a cross of those two breeds.
 
 
FWIW, a dog doesn't have to be a Chow to be worrisome.