I'm assuming that the systems and procedures have been in place since the 60's. If the system were that subject to false alarms, we'd have had a few other alerts by now. If the system is reliable, then the probability is high that this was deliberate. Whodunit?
- Some Hawaiian official, trying to make a point? Unlikely; it would require amazing stupidity not to realize that people could get hurt, and that this would be at best career-ending and more likely incarceration-beginning. (Hmm. We hear about people like that regularly...)
- China or NKorea hacking the system, probing to see what our response is like? If so, then they trust Trump a lot--that's kind of risky business.
- Anonymous or a script kiddie with a malicious streak? I'd vote for this one. I can very easily believe that the Hawaii government computer/network security is no good.
On the other hand, maybe Hawaii was trying to re-implement the old systems, and has a terrible test environment. That's really easy to believe too.
UPDATE: The story now is that during a shift change someone pushed the wrong button. From the rest of the story I get the impression that they hadn't been doing this very long. So, not software, but a klutzy system with no cross-checks. It was the second option, and they were trying to resurrect the system rather than re-implement it.