Unless I'm overlooking something, the demo only requires DOSBox to have a machine with predefined execution speed. There are no DOS interrupt calls that I can see. Other than that, the program could probably even be trivially modified to fit in a floppy disk MBR and could potentially run without underlying OS.

But there's nothing stopping you running it on a real DOS machine.

I expect someone will then say "though in practice today it's 256 bytes of binary plus a whopping 64kB of BIOS ROM and 16kB of video RAM" ;-)