This is very interesting, but I'm a little lost. UART is serial. Are they trying to get a serial terminal set up with some chip on this motherboard? Wat does it let them do?
Accessing the BMC UART gives you console access to the baseboard management controller's operating system (typically Linux-based), allowing for firmware analysis, debugging, and potentially bypassing security restrictions that aren't accessible through the normal management interface.
"X11SSH" is a Supermicro motherboard [1] with a (fairly common) Aspeed BMC implementing IPMI. (It has nothing to do with X11 or SSH - the name is an unfortunate coincidence.) The UART that is being accessed here is a debug UART for the BMC, which also runs Linux.
[1]: https://www.supermicro.com/en/products/motherboard/x11ssh-f