There has already been one appeal against the conviction and one of the grounds was the apparent inconsistency between one guy being acquitted and the other not. In the end, the appeal was unsuccessful, it being found that there was no inconsistency as the circumstances surrounding the two stories were very different:
McDonald met the victim on the street, and they got to chatting, spent some short time together, then got into a taxi and went to the hotel. His testimony says that the conversation started with something like "where are you going [girl]?" "where are YOU going?", and then things sort of snowballed into their having sex. It's claimed to be consensual, or at least as consensual as possible. At any rate, there are sufficient grounds to doubt that it was rape and a "not guilty" verdict" probably reflects that doubt.
On the other hand, the first time Ched Evans met or saw the victim was when she was naked in bed with the other guy. He'd come over to the room in response to a text inviting him there, and knew before he entered that there was "a bird" inside the room, and that they were having sex. When asked if Evnas could join in the victim apparently said yes, and so he did, and...
Regardless of the merits of the conviction of Evans, it is at least clear that the case against him, and the case that was made against McDonald, are different cases in many circumstances. The jury may well have found that the woman was able to consent to sex with the first man she met, but was in too vulnerable a position to say no to sex with the second man, and so Ched Evans could well be found guilty while clearing McDonald.
See:
https://www.crimeline.info/case/r-v-ched-evans-chedwyn-evans
the above is my summary of why there could be two different verdicts, the relevant paragraph in the document above says:
"Given that direction, it was open to the jury to convict both defendants, to acquit both defendants, or to convict one and not the other defendant. That was the point of a joint trial in which separate verdicts were to be returned. It was open to the jury to consider that even if the complainant did not, in fact, consent to sexual intercourse with either of the two men, that in the light of his part in what happened -- the meeting in the street and so on -- McDonald may reasonably have believed that the complainant had consented to sexual activity with him, and at the same time concluded that the applicant knew perfectly well that she had not consented to sexual activity with him (the applicant). The circumstances in which each of the two men came to be involved in the sexual activity was quite different; so indeed were the circumstances in which they left her. Those were matters entirely open to the jury; there was no inconsistency."
(applicant = Chedwyn Evans).