As I mentioned in this thread, I did assume that it was a mistake pretty much immediately after I got the message, but that doesn’t mean I haven’t been twitchy all day. This is apparently a pretty widespread reaction.
The first official statement that the alert was a mistake seems to have been in a tweet from one of our congresspeople (Tulsi Gabbard), whose office apparently had a better phone number to call than the rest of us. (The Hawaii DOD website went down almost immediately after the alert, so no information there.)