So McCoy kind of had a feeling Jim was back after that whole weird breach thing, so after the initial shock of being back had worn off, and he really sat down and thought about what had happened, he'd immediately left his room to try and find Kirk.

But honestly? He really didn't want to find him. There was only one reason why Jim would be back, and while he did really miss him, he didn't want him to be here. He shouldn't have to deal with something McCoy hadn't even really had a chance to fix yet, and no one should be stuck here against their will, without needing to be redeemed just because the Admiral had a bad sense of humor.