My vet did the same thing - gave me the big thing of puppy food. I ended up giving it to a friend. The secretary there told me it was a promotion through that company but that didn't neccessarily mean they were recommending that food.
Did your vet take a stool sample or anything? Did your puppy get shots. Sometimes vets (like doctors) aren't great at communicating - other times they really don't know that much about every breed there is out there. My vet is knowledgable about small breeds which is why I go there. He's been a lifesaver for me - I'm probably his most annoying customer, we've been there SO many times with Sandy since we got her
If you aren't happy with your vet, search around and find one you are comfortable with. I opened the yellow pages and called around, asking questions, etc. Didn't get anyone that minded
Hope this helps a little!