Is it possible my dog was badly hurt or abused in the vets?

My boyfriend's family dog has to have surgery in the new year. He is a 14-year-old Norfolk. He wasn't trained nor snipped.

He seems to be acting more aggressively since he came back from the vet. I said he looked scared and was acting differently. I was ignored, stating he had had surgery and he should be back to normal soon.

He cannot walk upstairs properly anymore, nor jump on the bed. He barks loudly to get up on our bed and we have to pick him up. We have 2 other male dogs. All untrained and snipped. You can imagine the house stinks of urine constantly.

When I moved in a few years ago, I roughhoused the dogs playfully, and I never hurt them. They are good boys. They never have gone to bite me unless I was way too rough. The one who has had surgery has gone for all the members in the house in the past few months more times than in the years I've lived there.

He also frequently fights and barks and the other dogs. And now my boyfriend tried to grab him to cuddle him, and, the dog put his teeth around his hand. My boyfriend (who can be very aggressive) was saying that his hand is stronger and something about snapping his jaw. My boyfriend doesn't show this side often but it took me by surprise. And when he like this, he is scary.

The dog then bit his finger, and it was bleeding heavily. My boyfriend is okay. After scolding him he threw a bottle of Pepsi and the dog. The dog is okay and is now lying on our bed.

What's happened? Has the dog been hurt in the vets? Is it old age? If it is abuse by my boyfriend and his family, wouldn't it have started years ago?