OP, your dog's sire is a bi-color. The person registering him with AKC just picked the wrong color. It happens, as often it can be hard to tell a melanistic black/tan from a bi-color, especially when young as pups of both colors will often have what are considered "bi-color" traits like tarheels and toe penciling. The difference is that on the ones who are genetically black/tan those black markings on the feet will fade and the tan markings will enlarge as the pup matures whereas on a true bi-color those tarheels and toe penciling will remain and the tan markings will remain the same, may even recede a bit, as it matures. But when very young, especially at the ages when most puppies are being registered with AKC (8 weeks or younger) it can be practically impossible to tell which color a puppy is unless you know the genetics of the parents and only one of those colors is actually possible.
So while his AKC papers may list the wrong color, that isn't an uncommon occurrence with bi-colors and dark black/tans, and it isn't a bit deal. Genetically he's a bi-color.