That seems crazy for him to be able to apply the code that way. Maybe as you begin to establish a working relationship with him you can convince him otherwise?
As far as OSHA is concerned, you are correct that it’s a 6′ drop for construction but it’s 4′ drop for general industry. Unless I am misunderstanding what you mean by “industrial work space”, general industry covers a wide range of activities but doesn’t include construction, maritime, and some others. I always have a fall protection fence for ret. walls at the 4′ level in anticipation of landscape maintenance activities. Obviously, I could be wrong.