Most of the lowercase abbreviations are just the names of device drivers or platforms. VK is just Vulkan, GL is OpenGL, ARB is “Architecture Review Board” as its sort of a preview or extension feature I think. EXT presumably for extension. KHR is Khronos, the organization that creates the Vulkan and OpenGL standards, and the acronym apparently means it’s “Khronos-approved”. https://registry.khronos.org/vulkan/specs/1.1-extensions/html/vkspec.html#extensions
Screen sharing infrastructure (for Wayland) in Linux was still in development recently. Maybe they just wanted to be able to use newer APIs?