Insider trading applies to the stock market. Changing jobs or employment conditions is a commercial matter only. Many people in companies abandon ship or take leave etc etc if they think the show is headed for the rocks or a big change. I once was involved in taking over a WA company where the senior execs x 5 all fronted the new owners with revised employment contract signed off a week or two before settlement.
Morally wrong in my opinion but no laws broken but we knew who we were dealing with after that and dealt with it accordingly