You accidentally briefly swipe left while unlocking, causing it to flash the camera, which causes the camera indicator to stay on for a while. You can reproduce it by locking your phone, touching the screen once, then swiping a centimeter left then back.
No guarantees—I’m no expert:
Turning off Face ID doesn't mean turning off the camera. Under "Camera," you should be able to see which app used it last. Settings > Accessibility > Face ID & Attention > Attention Aware Features and Settings > Face ID & Passcode > Require Attention for Face ID. Turn it off and restart.
You accidentally briefly swipe left while unlocking, causing it to flash the camera, which causes the camera indicator to stay on for a while. You can reproduce it by locking your phone, touching the screen once, then swiping a centimeter left then back.
No guarantees—I’m no expert: Turning off Face ID doesn't mean turning off the camera. Under "Camera," you should be able to see which app used it last. Settings > Accessibility > Face ID & Attention > Attention Aware Features and Settings > Face ID & Passcode > Require Attention for Face ID. Turn it off and restart.
No this is irrelevant -- he's just turning on the selfie camera by briefly swiping sideways. It's completely harmless.