I thought I could download for free I miss read but that does not change a thing, fact is the game is being made by someone using there time and skill to produce it. They have every write to charge for there work.
Besides if this is not free then I don't see what the problem is, if it was or had been free and those skins a reward on patreon then fine people still paying for it, If the game is not free and never has been free then people are still paying for the game and getting the content is fine.
I can only assume the people moaning are the patreon members who had it as a reward and now its free for everyone who has bought the game. I'm sure if I am correct they still get rewards purely for them patreon members.
Regardless don't remove something you made just because of some people moaning, Dev's game do what you want with it and if you charge for your work then who cares that your right as the maker.
I just hate seeing devs changing things just because the minority moans, it happened in mass effect 2 and 3 and other games up the age rating, cut content or censor it heavily.
If a game has extra content then fine, if a game has swearing, violence, sexual content, racist or homophobic content so what. This is life things should not be dumbed down or removed just because it upsets a small number of people. People are too damn soft and easily upset/offended into days world.