Workmen's comp question?

My b/f had a back operation about a year ago. He's been on workmen's comp this whole time. Yes it happened at work. Anyways he went to see a workmen's comp doctor in which he told him he could go back to work. I don't understand how one visit with this doctor determine that he could go back to work. He's regular doc. the one that has been with him the whole time from the time of his surgery til now says he is in no shape to go back to work. His doctor said it's going to take another 6 months. Can someone explain to me why workmen's comp doctor can do this without knowing anything about him? Can his workmen's comp checks run out even if he doesn't go back to work? I thought his real doc. would be the only one to ok him to go back to work. I don't think his employer would let him go back to work without his real doctors approval. I'm confused. Please help.

The workers comp doc already has all the medical records from the other doctor.

Workers comp fraud is rampant - including, having your personal doctor say you can't go back to work, when you can.

The reason you want a second opinion, is to balance out a biased answer. Since there are two contradictory opinions, seems to me like there's going to be an independent medical exam with yet another doctor, to give a third opinion.