If its a private business the boss can do almost anything.
Is this a private business? Because if so a ccw doesn't really have anything to do with it. He had a gun on the property of the business. In a private business you can carry as long as you have permission from the business owner/manager with or without a ccw.
There is no real damages here. A warning not to carry anymore. Sounds to me like his boss is trying to stop any lawsuits from the person making the complaint (unsafe work environment) and doesn't want to have issues with EDD.