I don't think a high color count matters if you can hardly notice it.
it looks like pixel art and it is pixel art.
No man, that's the way it should be, it's not an export error, that many colours is due to my pipeline.
On the surface this picture suggests a pretty small palette with the use of AA and dithering, but the Image Specs Tool tells us there are over 210 colours in the picture and a number of 1-pixel colours which seem to be artifacts. There may have been an errant problem during the export process. If you could see your way to replacing the file for this submission with the corrected image (and a different filename so the server can distinguish it from this present file), I would be happy to approve it.
It's a really cool painting! i wish to see more of this one day! but that many colors might be an issue, tho it can be easy to fix with the replace color tool, and i wonder how is your pipeline to get these results?