dog wont obey when called

Question
My boyfriend recently (about 6 wks ago) took in a dog that a second (or third?) family gave away. She is a German short-haired bird dog (liver colored) about 6 but maybe older.  My boyfriend is very frustrated with her because when he lets her loose in the yard he expects her NOT to go in the back marsh area to check out the rabbits and birds.  She does not respond when he calls her back into the house.  When she does decide to come back she is all wet and he yells at her and makes her stay on the outside screened porch.  the other day he got so angry at her he throw water on her back.  She hid at the edge of the marsh until I went out there, called her out, and she followed me onto the porch.
I was not there when he did this.  I have always been a cat owner, never a dog owner.  My friend claims that his system of negative reinforcement has always worked with his other dogs. I find this system cruel.  The dog is not mean but has been in different homes and so I suspect suffers from not being a. properly trained and b. not getting consistently similar commands during her lifetime.
He says he will take her to the pound or back to her previous owner.  At first, I felt that that was not fair to her, since I had originally questioned him getting a dog in the first place.  But now that I have thought about it, I feel that further mistreatment from him is wrong.
Am I misinterpreting his system of training? He claims that some famous Englishwoman/trainer(now deceased) encouraged negative reinforcement.
Thanks for your time.
Viviann

Answer
For the dog's well being, she would definitely be better off with someone other than your boyfriend.  Think about it from the dog's point of view.  If I come when I'm called (and I'm wet), I'm going to get yelled at, water thrown on me or left out on the porch.  Why would the dog want to come?  By yelling at the dog when he gets to him on the porch and NOT when he's at the marsh, he's telling the dog that coming is wrong, not that going to the marsh is wrong.  Your boyfriend clearly does not understand negative reinforcement.  What your boyfriend is reinforcing is the dog NOT coming to him.  Dog thinks, "If I come to him, I get yelled at, water thrown on me and left alone on the porch, therefore, I will avoid that negative by NOT coming."