Many mentions of a button being incorrectly pushed, however this is a computer system, not a manual system of breaking glass to push a button - which is so old school, it is almost obsolete.

In one of links, it says:

Miyagi, a retired Army two-star general, then explained that an individual on his team sent the alert in error, even clicking through a redundancy on a computer screen intended to act as a safeguard from such a mistake.

Rather then using the break glass analogy, (besides, who is going to put a computer system behind that setup) the computer program should require 2 person authentication instead of relying on a solo operator to make such a decision.

In other news, today Japan had the same type false alert, but it was stopped within minutes.

http://www.cbc.ca/news/world/japan-false-alarm-missile-north-korea-1.4489142