
At 3 weeks it would have been too early to have seen pups, even scanners who do nothing else but scan different species wont scan a dog before 28 days and most prefer a bit later.
I think your friend is right in getting the dog checked out again, an Xray will tell how mature the pups are, when skulls and spines are seen easily then there is usually less than 10 days to go.
When is the due date by mating? Was the mating witnessed? Could the bitch and stud mated 2 weeks later than thought, unless there has been a split season a bitch doesn't stay receptive for that long.
I think the the vet got the first scan wrong and with such a difference should have offered a second scan 2 weeks later.