According to the picture attached to this article, it just said "THIS IS A TEST of the National Wireless Emergency Alert System. No action is needed", so nothing particularly interesting.

It seems like 'presidential alert' is not actually the official name, and so it's probably more innocent than it sounds at first. I'm sure whoever invented it had nothing but the best intentions, still, I wonder who gets to decide what gets sent and when (according to the linked article: "the law also states that users cannot opt out of the presidential alerts, which are issued at the direction of the president — or someone he designates, or both — and executed by the Federal Emergency Management Agency"). What better way could there be to spread propaganda than through a message that all citizens of the country must read? And what could ever be so important that all citizens of a country that spans nearly ten million km² must know about it at once?

Edit: Honestly, the only thing I can think of is an all-out attack by evil Plutonians.