
If the dog hasn't been taught to do anything different then it will do what it wants :) Sounds to me like the owner needs to train the dog to wee outside , possibly by taking the dog out and using a specific word or phrase until the dog performs...we use *Hurry Up* ..once the dog performs give him lots of praise and attention.
When inside , the dog should probably be contained in a smallish area ...and then taken out for a wee at regular intervals. No punishment when he does wrong , but loads of praise when he performs well.
The dog is NOT old enough to know better unless he has been taught :) Speak to the owner and make him/her take responsibility for the dogs training