There are a ton of these cases arising now in Florida because of new "stand your ground" law.
Don't know the details of this particular incident, but there has been a sharp increase in these old farts, most of them irascilbe old coots, arming themselves and basically patrolling their property waiting on someone to come by so they can confront them.
Sometimes its a criminal and it is debatable whether it was wise to hold them at gunpoint. Sometimes its a freakin meter reader or a process server or what have you, just doing their job.
Some of these idiots have itchy trigger fingers.