Windows failed logins message: Glitch or always valid?

When I sat down to my PC this morning, I had the message saying there had been several failed login attempts and if I wanted to try again, type A1B2C3. It’s unlikely someone had tried to login without the passcode in the couple of days since I locked the PC. (People were here. It’s just unlikely.)
Can that message result from some sort of glitch, or does it mean someone did try to get into my PC? I tried looking at Event Viewer and Googling an answer, but it was all beyond my level of computer knowledge.

There do seem to be reports out there of this being triggered falsely, but in general, yes, it means someone tried some wrong PIN codes on your machine (or you left something resting on the keyboard or a cleaner came along and pressed a bunch of keys while cleaning your keyboard, or a stray cat walked across it, etc)

Just to head off anyone who might be about to worry that this is some horrific flaw in security - A1B2C3 doesn’t unlock anything, it just gives you another three attempts at entering the PIN - to slow down anyone trying to hammer the PIN number by brute force (as well as helping you understand whether you have caps or number lock set wrong)