No, this is a full-fledged GameBoy Color game, which is also compatible with the original GameBoy, running in a JS emulator.
You can also download the rom (.gb), play it with an emulator or put it on a GameBoy cartridge.
SDCC is a compiler that can compile C into GameBoy machine code and pack it into a rom.
GBDK-n is a library for accessing the GameBoy hardware in C.