Doesn’t really matter. Reason why Matt says that is most ChromeOS mountpoints have noexec flags and sadly most people aren’t very technical.
By telling them to login as chronos and escalate priviledges using sudo, it ensures that users stay within mountpoint that allows executing binaries.
You might as well just login as root, and:
mount -o remount rw /tmp
cd /tmp
curl [...]
etc.
This is different.
When you flash new SI_BIOS region, FSP needs to re-train the memory.
Until it’s done, you won’t see anything on the screen (in fact, you don’t see anything until EDK2’s GOP initializes the framebuffer).
You definitely shouldn’t interrupt it while it’s doing so, and display will come on after ~30 seconds and drop you into an UEFI shell.