I don't get it. What else is bare metal meant to mean? "bare metal" = "embedded system"? What does "embedded system" mean then? I guess my age / cloud-nativeness is showing?
In the embedded space, there often isn't any type of OS or kernel between the application code and the hardware resources ("the metal").
If I want to send out a character through the board's serial debugging port, I don't do an open()/write()/close(), I poke the UART's transmit register.
When they said "bare metal", I too thought they ran without OS which had been kind of cool.