"Running from within a motherboard BIOS" is waaaaay different than running from BIOS (aka Direct Boot). Before Windows, many games were playable by booting directly into them.
Before Windows, many games were playable by booting directly into them.
That’s not true. You’d boot up which loads the bios, which initializes your hardware, and then a Disk operating system like MS-DOS is loaded. From there you’d load your programs from a command prompt.
I think you’re right in inferring that OP is confusing DOS with BIOS but technically, plenty of old computers and early video game consoles like the Atari 2600 didn’t have a BIOS and would immediately execute the code on the tape, disk, or cartridge. Some old computers had bootstrapping but that’s not really BIOS in the IBM sense.
This is the least surprising one I’ve seen. coreboot just loads a payload and exits, so this is just a version of DOOM designed to run directly on the hardware (not using OS APIs). So basically, this is just DOOM running on a regular computer.