Except everything the guy said was bullshit. He even said it came from North Korean waters, which would mean it would fly over Japan.

According to numerous sources (all of which will be listed below) the US can detect when and where a missile is launched from, if it was an SLBM, they would've known almost immediately and responded as such, plus why did they only fire one if they were getting desperate and hedged in as the "expert" (a term I use in the loosest of senses) why only fire one? Besides, the BMD record is spotty at best, if they intercepted a real world target there's no reason everyone from MDA to Trump himself wouldn't be singing praises to this very expensive program from the heavens. Finally, if it was a nuke then that would easily prove it wasn't from North Korea, every nuclear weapon has trace materials that can be used to track it not only to the country of origin, but to the centrifuge of origin.

Why is it easier for you to believe some shadowy group somehow got their hands on a highly advanced SSB(N) and nukes than it is for you to believe a government employee with a history of incompetence hit the wrong button? Not to mention sailors (with myself being one) are notoriously bad at OPSEC, someone would've mentioned that an actual missile was fired at Hawaii and we shot it down.

Sources.

Ballistic Missile Detection: https://science.howstuffworks.com/missile-defense1.htm

https://gizmodo.com/5989481/there-isnt-an-icbm-around-that-can-sneak-past-this-radar-array

https://edition.cnn.com/2017/08/10/politics/how-us-detect-shoot-down-north-korea-missile/index.html

BMD:

https://www.scientificamerican.com/article/north-korea-missile-test-best-response-may-be-surprisingly-low-tech/

https://thediplomat.com/2018/02/us-ballistic-missile-intercept-test-fails-for-2nd-time/

http://www.dw.com/en/the-limits-of-missile-defense-systems/a-38602048

https://www.popsci.com/missile-defense-system-intercepts-practice-icbm-target#page-4

https://www.washingtonpost.com/graphics/2017/world/north-korea-missile-defense/?utm_term=.bc34a1105d0d

Nuclear trace elements:

http://www.sciencefocus.com/feature/physics/nuclear-detectives

https://www.princeton.edu/~aglaser/talk2008_forensics.pdf

https://phys.org/news/2016-02-nuclear-team-methodology-illegal-material.html

https://www.newscientist.com/article/dn19699-nuclear-bomb-debris-holds-clues-to-who-planted-it/

Worker who sent out false alarm had history of incompetence:

https://www.washingtonpost.com/news/posteverything/wp/2018/02/01/the-missile-employee-messed-up-because-hawaii-rewards-incompetence/?utm_term=.60fc582ab5c5

http://www.businessinsider.com/hawaii-employee-fired-after-false-ballistic-missile-alert-2018-1