I think it's plastic with a rubbery coating. I definitely don't think it's an animal product. That would be weird for Tesla to put leather on seat backs, but vinyl on seating surfaces.
What did you try so far to clean the scuffs? A Magic Eraser might be the best thing.
But, you may have scratched off the rubber coating. If so, you'll probably have to replace the part to get it to look perfect. You may be able to put some touchup paint of some kind to get it to look better, but not perfect. Tesla vendors also sell form fitting coverings for the seat backs that protect them and hide any imperfections.