But your link says that QuakeC was a compiled language

QuakeC was compiled into QuakeVM bytecode, which made all modes and logic portable between platforms without having to recompile things everytime, unlike what had to be done for Quake 2 (which was 100% native code).

This hurt performance a bit but in the longer term benefited the modding scene massively.

It's compiled into bytecode, so it still requires a VM / bytecode interpreter (whatever you want to call it).

Compiled to bytecode.