Which languages with a full runtime and memory management are in the same ballpark? Go, maybe? Obviously these are unimpressive figures for unmanaged languages.
To demonstrate the OS's capability and relatively small size, in the late 1990s QNX released a demo image that included the POSIX-compliant QNX 4 OS, a full graphical user interface, graphical text editor, TCP/IP networking, web browser and web server that all fit on a bootable 1.44 MB floppy disk for the 386 PC. https://en.m.wikipedia.org/wiki/QNX
On the one hand, if it's genuinely self-contained (that is, it doesn't expect a .Net runtime to have been preinstalled on the OS), that may well constitute an improvement over previous iterations of C#.
On the other hand, the smallest executable I can find on my system occupies 6K and actually does something useful.
On the third hand (said the octopus), if all we cared about was executable size and efficiency, we'd still all be coding in assembler, or at least C or Forth.