I heard there was a planned test of the emergency alert system in the United States today, October 4, at 2:20 PM. To avoid being disrupted, I turned off all alerts in Settings -> Notifications (one of which is actually labeled "Test Alerts").
However, I was quite surprised when, at 2:20, my phone still showed the alert, vibrated, and played a loud sound despite being on silent with all alerts off.
Why did my iPhone not respect my choice to have emergency alerts turned off?