this is a dillemma and sad to me as I have commissioned the piece and also replied to the comment who accused me of using AI. I believe its bleak when people accuse real artist illustrations of being AI. It takes away more from artists than it does from AI. Imagine an artist spending weeks on a piece and people label it AI with no proof whatsoever.
I saw the comment and I am sorry you had to go through that. If it helps, you can consider mentioning anywhere on your game's page that it was a piece you had commissioned from an artist, and link to the artist's page directly. It might help curb these comments from your future games.
I edit photographs for my backgrounds and link to the photographers' pages directly. That way people will know they were photos edited with Photoshop, and not AI art, so I don't get those comments.
I still remember someone accusing me of using AI(P) for my profile image when it's actually a Clippy render from the Windows XP era with a Randy Qubit hair crest, modified with Game Maker's paint tool.
This anti-AI(P) paranoia has become especially serious now that AI-Art is achieving increasingly better results, and due to the lack of noticeable differences or transparency regarding its origin, there is no longer any trust.