He is consistent, all functions have that keyword, it's his codebase. He has also has the api(custom) define so his metaprogram knows which functions to publish into the plugin system. C++ syntax is not very regular so if you want to consistently catch all functions with a homemade parser or grep or whatever it would need to be complex, it needs to do backtracking, account for stuff like operator+ etc. If you do what he is doing it's trivial to make a metaprogram for C++ that would consistently catch all functions.

It's great that you would fail a code review in your company for that but it's not relevent.