I think the N.G guys are doing meta gaming because i think they got idea that malabunta's are coming from South gate. Secondly they have to ask ' sir what you need ' before start shooting. They didn't ask anything and start firing. Lastly i even didn't see that any N.G guy put a radio call to other officers that malabunta are in base and all are waiting for them at south gate.
I see you lack some information about Fort Zancudo and its territory. There are two zones - Red Zone and Yellow Zone.
Red zone is basically inside of Fort Zancudo starting from inside of North gate and south gate. If you cross any gate and enter base, no NG or any legal org gonna talk they just gonna shoot on sight.
Yellow zone - In this area, NG and other legal orgs have to give demand to leave area. If you do not follow demand or leave n comeback, they have more than enough reason to shoot you.
For south gate, yellow zone starts from area right out side south gate till end of bridge.
For north gate, yellow zone starts from area right outside north gate till road that joins highway.
About Metagaming, if you are stacking up at one gate with 6 cars with same color ofc NG going to give info through either text radio or voice radio. Just because you did not see head tilting animation does not mean they MG.
There is thing called department chat aswell. If they see 6 cars with same color stacking up near one gate, ofcourse they are going to ask for help because they are about to get raided.
Have a nice day.