Experienced Airsofters don't notify their neighbors and/or local branches of Law Enforcement agencies about games on privately owned land because it's fun.
This is dumb.
Anyone involved in this really ought to wake up.
This is scary Real Life™ stuff.
You may have gotten away with it because Police knew and trusted that it was all part of a nerdy zombie thing, but they definitely were not happy about it.
All Airsoft vs. Public stuff aside, you really wanted to risk the future of a Food Drive?