Hey thank you! I'm glad you liked the game.
I appreciate you asking outright. As far as I'm aware it's not, this was made by a different artist than the rest of the project's art, so it probably looks a bit different. But now that you mention it, I'm not sure anymore, so I'm replacing it with one I know for certain is not AI. I'm going to look into it.
Edit: I was not able to 100% confirm whether or not the image in question was made using any AI. I'm keeping the current image for the time being.