It’s literally in the link. A non-specified amount of code in the MicroW8 runtime which isn’t included in that 256 bytes to implement the graphics layer (320x2

It’s literally in the link. A non-specified amount of code in the MicroW8 runtime which isn’t included in that 256 bytes to implement the graphics layer (320x240 256 colors 60hz) and gives you 256 kib of memory. 256 bytes is the “cartridge” to run on this platform with compression. It’s still extremely impressive because of the creativity of the generative visual effects they figured out how to fit in 256 bytes.