Not a request for help, but an explanation?

Yesterday, I installed the latest kernel in my mint MATE 20.3 desktop here. It advised me to reboot, so I selected the reboot option after closing all programs, and away we went. It rebooted fine and I got a login prompt, that looked oddly different. I think it had my full name instead of nothing above the login prompt.
And no matter what I typed in as password, it wouldn't accept it.
Thinking I might have to repair something from a live installation disk, I decided that at least a hard reboot might be worth trying, and with a proper power off it rebooted as normal.
Anyone have a clue as to what that might have been?
I am the only user on the system. It's mine, all mine, and one else ever uses it.
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Ideas are more powerful than guns. We would not let our enemies have guns, why should we let them have ideas?
Josef Stalin