The farmers involved made a decision based on gut instinct and frustration. Were they reckless? The man who ran away had a gun, presumably for disposing of the sheep. As police have warned, it is a situation that could turn ugly.
Farming's tough - sheep are valuable and the gun disappeared with the coward who ran off.
Farmers are practical people - faced with the option of noting down the registration number and calling police, they chose to deal with the incident at a safe distance - who can blame them?