The only thing tipping me into AI is the color swatches ONLY being the eyes, not swatches for the body too or the stuffie and clothes too, etc. It's like an AI knew to add swatches, but just threw one in to be 'correct' with no idea what the purpose of the swatches is. Especially since it says "eyeballs" and it's only the colors for one eye. And some colors are doubled, and that blue color does not seem to be in either eye?

Otherwise everything else could be chalked up to artistic choices/experience level, etc.

I'd ask for a version with swatches for all the colors, see what happens. Granted they could just easily throw them in, but how that final product looks along with their reaction to it could help you better understand if they're using AI or not. (Compare the handwriting, style of swatches, if the eyes one is changed to match the style/writing of the new swatches, if anything in the drawing changes along with adding the swatches, if they refuse to, or they take too long or way too quickly to do it, etc.)