Is momma still allowing them to nurse?? if so, he may just be having enough... my pups are 10 weeks old, and momma still gives them a treat once in a while...
I started mine with a mix of nutro canned food, and crumbled dry food, with some puppy milk and water.... then canned with whole dry food... now they decided they will have only the dry... so I am happy... it took to the little girl a bit more to decide to eat...
Hope that helps... I would keep an eye on him, as for liquids intake...
Good luck, this little ones have a mind of their own, and can be stubborn!