Concerning this page: Introduction to C++ Programming in UE4 | Unreal Engine Documentation
Non-UObject References
Normal C++ objects (not derived from UObject) can also have the ability to add a reference to an object and prevent garbage collection. To do that, your object must derive from FGCObjectand override its AddReferencedObjects class.
>>> I think that what was meant here was:
To do that, your object must derive from **FGCObject **and override its AddReferencedObjects method.