So now we're examining the authority to use force (since we're discussing vigilantism).

The shooter in this case, acted on (what turned out to be) a false report.

Not to get too hypothetical but, if the shooter had not been the husband, but Officer Bubba, who noticed the couple in the pickup truck, and the woman reported rape... would HE (as a representative of the people/society) have been righteous in shooting at the alleged rapist?