Because a lot of discussion orbits this aspect, I would like to give my two cents about the morality of buying a product made by someone with morally reprehensible behaviour.
Even if very remote and small, I believe that doing business with an immoral actor can be considered a kind of cooperation with evil; at least in so much that if no one did such business, the actor would have more trouble or be completely unable to keep doing evil acts. This is not meant to imply anything other than that, however. In particular, I am not saying we should investigate thoroughly every shop we buy from, every brand we purchase products from, every cashier the we interact with, etc. This is not something we have a moral obligation to do, and in fact can be immoral in that it would be intruding into the privacy of these people.
My point in calling this cooperation with evil is to further distinguish how we can deal with it. One distinction is whether the cooperation is direct or indirect. Direct cooperation is when our acts are directly helping the evil they are causing. For instance, if we buy diamonds from someone who employs bad labour conditions or maybe even slave labour to get these diamonds, we are directly contributing to this specific evil. On the other hand, if we buy books from a company that publishes immoral books, but we are buying books that are perfectly fine, then the contribution is indirect.
Now, the importance of this distinctions is this: If what the people you are aiding are doing is inherently evil, it is something you absolutely can't aid directly without doing evil yourself; even if it might be considered something minor, like stealing only a little money or only telling lies. On the other hand, if what they do is situationally evil, or if the aid you give is indirect, it is possible to consider pros and cons and decide to contribute with the evil due how double effect works, it is possible to do so without doing a moral evil, if only because you expect to extract a greater good out of the cooperation. For instance, you might dislike several policies of the Amazon company, but still buy with them because the alternative would be not having access to a really good book.
Of course, when we are talking about games, the good effect you might extract is rather limited. There is not shortage of good games out there (even if you need an emulator or a patch to run them in modern systems) and entertainment is not something inherently that important in first place.
My point is, refusing to buy Caves of Qud by the actions of the dev is not a weird position, and I think it is really the best one. But either way, we shouldn't badmouth CoQ with lies. If someone hates its gameplay, I think that person has a right to say what they think, but I think Qud actually has very good design and ideas, and it is a real shame its devs are such weirdos.
