I had the exact same issue this morning with my Apple Watch Ultra 2 (WatchOS 10.2 (21S364)):
It started when my AWU2 switched the lights on in my house via Homekit (I have the Home App as a complication in the watch face).
After that I was not able to attend a phone call because the display was unresponsive. Tap gesture didn't work either. Then suddenly the keypad opened and the watch started dialing.
I couldn't stop it, so I took the watch off to lock it. But then the it started entering pin-codes and lock me out for 1 minute then 5 minutes... This caused a little panic... I thought I'm hacked...
Then I solved it for now by doing a reboot pushing the crown and the button below on the right side at the same time for a couple of seconds, until the watch goes off.
After starting the watch again, everything was fine. (I had to wait the 5 minutes to pass).
Hope it's only a software thing and it will be fixed by the 10.3 update tonight.
And I'll remove the Home App from the watch face. Otherwise it'll maybe open the garage door next time... ;-) - Lesson learnt.