I think I triggered this a few times; I use a alarm clock that's dismissed via math equation which I frequently get mixed up with the lock screen when waking up. I have GrapheneOS set to auto-reboot every 8 hours so then there's also the SIM unlock screen. In the state of just waking up it's easy to PUK lock the SIM. I guess I just assumed the "Pixel is starting" message was some unrelated bug and just manually restarted. I think you can still continue to a normal boot if you manually lock or wait for the lock screen PIN timeout to expire.