If those bugs are only present in the Linux port, then yeah, Linux users cost more to support. But if a significant amount of these bugs affect all platforms, then you could argue that a Linux user is much more valuable to them than a non-Linux user because they provide better feedback. Assuming they actually care about fixing their product.
Part of the problem is that Linux isn't really one platform, it's 10 different ones of varying popularity (e.g. supporting Gnome on Debian with Wayland doesn't mean that KDE on Nix with X will work). And it costs somewhere in that 1-10x range to support it because of that.
yes, this. i don't know if it was the same game another another where the devs said that while linux users send the most bug reports they are also the most grateful about having a game that runs on linux, and all their reports genuinely helped make the game better for everyone. (wildly paraphrased from faint memory)
in other words, if you want your game tested and get good feedback for it, do release on linux. maybe even release on linux first. linux users will love you for it, and you get to release a more polished game for a wider audience on windows.