Hey there...
We just recently got a yorkie from a puppymill, where she was used maily for breeding. We've had her a little bit over a month and we went through the same stuff as you have and are going through, but Trixie never *snapped* like that. I woudl say its very normal for him to do this, considering his past. These babies were not and still is not used to the attention, love, and so forth we are giving to them now so that's why they are in fear of *change*. I will say that after a month, Trixie is more than coming out of her shell--shes eating, sleeping, playing and having her personality come out more and more each day! She is still a bit skiddish of *any* strangers-especially men.. so thats gonna be an issue for a while. I would suggest just keep introducing her and socializing her as that's the best way to get him *use* to the new life he is gonna have now!
Congrast on getting your baby
. How old is he?