The humor comes from the bewildered or concerned reactions of the teacher and other students who believe they are witnessing a real crime. Popular Video Examples
In these videos, the "troll" joins a random online class and stages a dramatic event that unfolds in the background of their camera. The "My Car Gets Stolen" variant typically follows this sequence: Trolling Zoom Classes... But My Car Gets Stolen
You can find variations of these high-stakes "but then [X] happens" pranks on YouTube: The humor comes from the bewildered or concerned