This mod is not a creation, it's just a repackaging of 2 old LE mods ported to SE: Masque of Argonian Vile and Masque of Khajiit. Reporting bugs is not going to change anything, as the original MA is not involved.
You're all reacting like you're discovering Masque of Argonian Vile for the first time. It's been in the STEP SE Guide since the beginning, and it's been in the STEP LE Guide before from way back when. It's had this same different neck texture all along.
Perhaps you should consider dropping the Masque of Argonian Vile mod from the guide, and ignore this one, if you find it's no longer up to the STEP standards. Including such singular, niche mod in the guide is weird - IMHO, similar to Lucien Lachance. I suggested to replace it with this mod so that there would be a Khajiit version too, for consistency and balance of weirdness.