People often do what they love with the tools they love. Complaining that someone wrote a hobby project with C is akin to complaining that your neighbor made a decorative baseball bat with her lathe instead of a 3D printer.
Writing Lisp in 200 lines of Haskell wouldn’t be nearly as interesting. The whole point is (presumably) that it’s fun to code golf in C because it’s not very expressive. Relax, no one is going to use the OP’s code to run a pacemaker.