There's no threatening involved. My actions would be a REACTION to gunfire. No premeditation whatsoever. The only threatening would have come from Wyatt Earp.
You ought be very careful of the threats or assertions involving the use of a firearm because you CAN lose your right to own one for just such irresponsible demonstration. The man made a decision to use deadly force against two animals he perceived to be an immediate danger. In most states, unless you are sure the gunfire is or has been deliberately directed toward you, any intentional aggression you make toward him with a brandished weapon could render you a felon, whether you use any force or not.
You seem to think that the second dog was killed in its owner's back yard. It's more likely that both were shot in "Wyatt Earp"'s yard, then one managed to wriggle back under the fence before assuming room temperature.
Hearing gunfire on your neighbor's property is NOT sufficient cause to start shooting at people. It would not be self-defense, and would be considered negligent homicide at the very least.
And you have to gall to call someone else reckless. Wow. Isn't it better for those armed to have some idea of why and what they are shooting at? We're not talking the streets of Sadr City, after all.