Conspiracy theorist here and I think that there where Threats to both Japan and Hawaii. Seems like a massive cover up to keep the world calm. Which I wouldnt mind because Nuclear war with the current highest threat is a no win for anyone.

One theory is a test to see how the public would react, to make sure there isn't mass panic, hysteria and crime.

Japan had several actual missiles fly over in the recent past and not much happened besides condemnation.

Haven't heard about the Japan false alarm issue. If there were "coincidental" false alarms to both I'd be more inclined to believe these were just threats that were taken care of.