First off, I am not accusing the dev of anything what follows because I have no proof for anything.
But if (and only if) some of the accusations of fraud are true, then I tend to think there's a simple reason for not providing a linux version. RenPy is just a python framework, and you are actually able to inject arbitrary python code into RenPy games, or even replace the binaries with patched ones. Trust into RenPy games is high, because you basically always have false positives and never actually any virus in these games. False positives come along quite often, but there are easy ways to circumvent them, otherwise the devs wouldn't be able to resolve it. True positives can only happen for viruses the antivirus providers already know about, so new viruses simply are not detected until they know about them. What could (I repeat, could) be the case here is the following (which is, I repeat, just a theory not based on actual facts): the dev wrote a virus for windows and only provided a mac version to provide an alibi, because he couldn't write a virus for the other platforms, and linux people are more techie than mac users and would probably spot such things, even while their market share is far below those of mac users.
Just a theory. Not based on facts. If you hop onto this train, make sure you find proof before saying anything. I am just saying this so people with better analysis skills than mine might want to take a look into this and proof or disprove what I'm saying.
I am not saying the dev is actually doing this. But I started to think it's a possibility after reading how he's behaving.
Keep calm. He's not guilty unless proven otherwise.