Why is my son using a different passcode to approve more Screen Time on iPad?

My son can open an app, ask for more time, and input my old “unlock iPad” pass code to approve as much as he would like. It is not the same code as the one I’ve set for his screen time pass code, and I’ve tried resetting it several times, as well as rebooting.

Any ideas? Is this an actual bug or am I just missing something?

[Re-Titled by Moderator]