You do realize that the article highlights the fact that regardless of the employment of the officers involved, the argument is being made that "an operation" was conducted as NEMLEC, a private corporation not beholden to open information requests.
Off duty officers shoot people. Some times they are just acting as private citizens. Sometimes they are uniformed private security. Other times they are just plain old moon-lighted security. The legal protection carried by the civil police force to the officer varies under each of these scenarios. The actual police force that the officer is on the payroll of is "usually" not obligated to defend the officer under any of these considering the scenario of a lawsuit, wrongful death, civil liberties, or misconduct. Further, there is usually some Union (non-government entity) involved with similar obligations/exceptions for defending the officer.