How would you run Node on it otherwise? If it's not running an operating system that Node already supports, it means they've done the very large amount of work

How would you run Node on it otherwise? If it's not running an operating system that Node already supports, it means they've done the very large amount of work needed to port a Javascript interpreter to a bare-metal environment. I'd be highly impressed if they had actually managed to do that, but I'm doubtful. More likely they are using some stripped-down Linux kernel and userspace. A combination of uCLinux and BusyBox should work rather nicely.