Since insurance is state-specific, and I suspect your neighbor probably pursued it to the limit, this probably doesn't apply but....
In most states a homeowner's policy has coverage for "personal property" and also "personal property at a 2nd or another location". Here (CA) most policies include 10% for property at another location. If you have 150,000 coverage for personal property at your home you could use up to 15,000 for property at another location. That limit can be raised for additional premium, but 10% is what's included with no additional cost. It covers stuff stolen from your car when it is parked at the airport, or taken from your hotel room while you are on vacation, or burned in a fire at your mother's house 'cause you had it there until you brought it to your house, or stolen from your barn at your distant property.
Since he apparently tried filing a claim with his insurance company this appears to not be the case in NY but it surprises me as I actually thought it was pretty standard across the country.
We DO have "basic" policies available that don't automatically include that feature (and other features, like liability), more like an "ala carte" thing where you buy each individual coverage rather than the normal "package" policy. Anybody that contacts me only gets a package policy (unless there are other problems disqualifying them from the preferred companies and package policies). A package policy is less expensive than a basic policy with all the other necessary coverages added.
And as far as the lockable shipping containers go, our archery club has had them broken into twice over the last few years. We finally modified them with a solid bar across the back, slid into slots on each side with the lock totally surrounded by a steel box except at the bottom where there's room to get a hand and key in. So far, so good. You'd have to have an oxy-acetylene torch to get in now, but we realize that someone may try that next.
Phil