We don't have laws that forbid photography (except at specific military installations or contractor sites) - to the contrary, photography is a protected activity that the government is not legally entitled to inhibit, even if it tries (the government will always lose at trial if it goes that far).

While a private company can limit photography of its property while you are physically on its property (ie an airline can forbid photos of the cabin, seats, etc while you are on board, but cannot stop photos of its equipment while you are located on public property), taking photos of AC equipment while standing on public property (which an airport in the US is) is perfectly fine no matter how much they protest.

My advise is to do whatever is necessary to identify and call out this employee on the Internet (ie Facebook, Twitter, etc) and perhaps they will be shamed or advised by management to cool it and keep a lower profile and more helpful attitude.

There is nothing stupid about taking photos at an airport - many of us do it all the time.