If a private facility asks the governor of the state to give a speech on their property that is open to the public at large and the governor is speaking in his official capacity as the governor, then the facility for all intents and purposes is public property and people on the property enjoy the same rights and privileges they would otherwise enjoy if the event were to have occurred on public property.
In this case, because of the public and political nature of the event, the private property became quasi public property and the church ushers who assaulted the cameraman were acting as quasi officials of the state.
If this were a private political event, then what the heck is it doing in a church?
Governor Kitzhaber does not have any “official capacity as governor” since he left office.