..snip..
Another diver came and pointed out that his inflator hose had come loose and then swam off.
To answer the OP question that diver, in my opinion, did the wrong thing also. If you see another diver having difficulty under water it is your duty as a good diver and a human being to try to help them out. The assisting diver should have signaled his buddy to come over and help also. That is like seeing someone pulled over with a flat tire and stopping to tell them they have a flat tire then driving off. Is it an emergency? No, but it still makes them an a$$hole.