That was initiated through the Integrated Public Alert Warning System which is a multiple delivery platform system.  Emergency Managers/Civil Defense Officers who are certified can use a relatively friendly program to blast a message to all cell phones, TVs,  radios, NOAA Weather Radio devices, and eventually more in an impact area.  A single user went rogue & sent a false alarm.  That user has since been reassigned far away from the IPAWS console.

Typically most US folks see IPAWS triggered for severe weather events.  That is its most common use.