
Since the puppy passed woms it would suggest that it's not been very well cared for before your friend took it on :( As far as I know, most modern wormers show no evidence of actual worms so I'm guessing this little mite was infested :(
Perhaps he's not used to being fed much either which, coupled with a heavy worm burden, will possibly mean his tummy can't take much as yet.
I'd leave off the Beta puppy for now and feed steamed white fish for a couple of days and then boiled chicken for a further couple of days. This will be gentler on the system. If the puppy shows no sign of improving in the next 48 hours at most, I'd return to the vets as they can go downhill so quickly.
Was it your friend's own vet that give the pup it's vacs or was the puppy done before being bought by him? It may be that this puppy will need to be more closely observed than most - even if apparently lively just now. To not want to eat is abnormal - even allowing for strange surroundings and trauma of leaving litter mates / dam etc
Hope this helps. Teri