Ok I got it now.
Everything is clear now and thanks for taking time to explain me the “hierarchy”.
I was confused by the fact that my BP will be called first then my C++ and I don’t why, I thought that the Parent Class can have a BP in between which is a non possible at all 
If I understand also properly AddCallToParent will go in the hierachy to find the code to run. It could be a parent BP or the C++ parent class.