Uhh...no tobiano does not generally leave the head solid. You need to do a little more research if you are going to act like you are 100% sure. Now you can have a splash tobiano, but it is not from the overo pattern. What you are saying would make every horse with a face marking from the overo gene? That doesn't even work. Since this horse is a paint cross... APHA.Com - The Breed
They have all the patterns on there.
What were the parents of this horse? The only way he is a tovero is if the sire or dam were a tovero if he isn't full paint or a paint/pinto colored horse cross. Both parents would have had to be tovero or one a tobiano and one an overo. So i'm guessing he's half paint half "some solid colored horse...not paint bred".
Let's just say dad was solid and mom was a tovero. The resulting foal would have a better chance of being a tobiano than a tovero...it's hard to pass it on like that, but it's definitely possible.
Anywho, as said before he could be a tovero, but tobiano is more likely. He sure is cute though.