Tom, I'm not doubting that this could have been an officer, but it seems very odd and out of character. I strongly urge you or your DIL to file a complaint with their inspector general:
FWC - FWC Inspector General
If that doesn't get results then contact the Governor's office. I can guarantee that in an election year you would get results and fast.
If someone did call in a complaint then there is a record of it and the officer that was dispatched. If it was an officer then they should be reprimanded for that kind of behavior.
Also it's not necessarily a gate code, some gate systems respond to the "chirp" or fast on and off of the officers siren. In a life or death emergency those are generally the better option.