This is because chromebooks run on an operating system called "ChromeOS", you cannot download games on it from anywhere but the play store. At least not reliably. I would recommend getting a refund, because as far as I know, this game only works on Linux and Windows.
first go to chrome://flags and search vulkan then enable it and restart your chromebook. check if it worked at chrome://gpu and look for Vulkan and it should say Enabled next to it. Then rename the file to BuckshotRoulette.x86_64. Search how to turn on linux for a chromebook and run the command: chmod +x BuckshotRoulette.x86_64