How did an unauthorized number call me with DND filter engaged?

I utilize the Do Not Disturb focus filter every evening at bedtime, running until a certain time in the morning. I have designated specific apps that can send me alerts and specific contacts that can contact me during this DND timeframe. This has always worked properly, until last night. One hour and 23 minutes after the DND focus was engaged, I got a cell phone call from a number not in my Address Book and most certainly not on the list of numbers allowed to pass through the focus filter. I answered the call and it was a spam call telling me they were a delivery service, calling with a delivery because no one answered their knock at my door. Totally bogus! There was no knock. There was no one at my door. I have security cameras. My question is How did an unauthorized number call me with the DND focus filter engaged?