Does anyone know why one of my Shiba Inu's puppies looks different from the other two? (Smaller, rounder head and eyes) he also acts a lot different, he's more timid and easily distracted. He's in the last picture

For context, we got the mother from a rescue who got her from a breeder in Louisiana, and the breeder didn't tell them she was pregnant, so nobody really knew. The puppies are all doing fine, but one just looks different. He's the one I'm trying to keep, since he seems to be very attached to me (and we aren't going to sell the other two) so it isn't a money thing, just curious. All of the puppies will be going to a good home with people we trust. Also, Mama's doing great so far, still learning to be a dog though. Help much appreciated!