To be fair, if you go to their website it does say that you can also use SMS, but there’s no mention of that on the message that was displayed on the train.
https://www.ns.nl/reisinformatie/voorzieningen/veiligheid-in-de-trein-en-op-het-station.html
@Brendanjones The only way I can get emergency information in my small town is through Facebook. I don't have an account so half the time I'm trying to find out why power is out or whatever I'm blocked by a login screen.