It was the tech handling your puppy and telling you he'll be aggressive? If so, I might agree with the advice that says keep the vet (if you like him/her) but request a different tech. But I'd also be questioning whether the vet agreed with the tech, since it seems they didn't object to what the tech was doing. The tech handling your puppy like that is a great way to make it a self-fulfilling prophecy that he'll become aggressive.
And do not take away his bowl and put your hand in there to take food. You got lucky on your first one. This is a great way to CAUSE food aggression.
I agree with this also. Simply messing with your puppy's food and bowl while he is eating is almost guaranteed to cause food aggression. Much better to give him treats while he is eating, or in exchange for taking the bowl. This way he sees you as bringing good things while he eats, not just pestering him.