I doubt the attorney would say that if there is proof otherwise. I take this statement to mean there is no proof.
It was pointed out on another website by an attorney discussing the case that none of the racist claims were brought up in the trial, but the charges alleged such a claim.
He said this is often a dirty trick a lawyer pulls to get the case into court where the prosecution can beat on the defendant for awhile, but doesn't have to prove the claim that was the basis for filing the case in the first place.
Now we can see that one of the reasons no such claims were made was because the judge didn't allow it. Since the Defense attorney denies his client said it, and since that probably means there is no evidence that his client said it, the only evidence they could have must be social media messages or some such.
Depends on what counts as evidence in your eyes. Their partner-in-crime, Roddy Bryan, testified to the police that he did. So sure the attorney denies that McMichael said it; doesn't make him look very good. It's a he said/she said situation which may or may not have been completely in character for McMichael. Regardless, the prosecution felt confident enough in the evidence to want to introduce it during the trial but the judge denied it.