I'm japanese.TBH for a long time i had thought this was a parody account. Around the time of 2011 3.11 earthquake, the NERV Twitter account(the origin of this app) gained popularity and reputation as a reliable source of information in the social media space (At that time government official information provided on Twitter was extremely little).

I guess a part of the reason of its popularity today belongs to otaku culture on the Internet that was a good fit for this kind of anime-origin stuff. Plus the company that runs NERV is owned by Sakura-Internet, which is one of the biggest computer infra business, and is believed to provide a reliable system at time of emergency.