Acetone is an organic solvent the same applies to the nail polish. They can't react with metals or any inorganic compounds.
I hesitate to wade into this convo at all, but once upon a time I did get a degree in chemistry and then some time later I did get a doctorate in materials science, and there are a few misconceptions I think I can speak to.
First of all, organic solvents react with inorganic elemental solids and inorganic compounds all the time. The text quoted above seems to suggest a belief that chemistry doesn’t exist across that boundary, but it definitely and extensively does. This includes acetone, which has known chemistry with a number of divalent metals. Generally speaking, it would be non-reactive with aluminum (and is used to remove organic debris). But I would not assume it would be non-reactive with all aluminum oxide surface coatings.
Second, aluminum alloys that are heavy in Cu content will actually become photoreactive in the presence of light, acetone and moisture. The 7000-something series Al alloy in an Apple Watch shouldn‘t have this problem (I believe the alloying metals are zinc and magnesium). But still, the fact is that there ARE reactions that can occur between aluminum alloys and acetone.
Third, the acetone found in nail polish remover is not going to be any sort of reagent grade solvent. It’s going to be a low quality acetone that’s bound to have all sorts of contaminants, including potentially HCl. Chloride-contaminated acetone could easily lead to a corrosion situation with a metal that would normally be rather impervious. I would think raw aluminum could easily pit. The watch probably would be protected by its oxide coating. I wouldn’t care to try it, myself.
So, if I have fulfilled my quotient of useful information pertaining to the specific original question, let me now say that in my experience as an Apple Watch user since Gen 0, the unperturbed casing will long outlast the rapid obsolescence of the internal technological guts of the watch. I don’t think there’s much benefit from going to any extreme measures (any measures at all, really) to protect a sports watch from sports activities.
OP, there is not a lot to gain and quite a strong potential of a damaging oopsie for what you’re contemplating. If you’re determined, lucky and careful, it probably won’t make a difference in the durability but likely won’t do harm.
When it comes to science experiments of questionable utility, YMMV according to your own whims and tolerance for “oh ****” mishaps.