Scene vs Content Browser references


I’m new to Unreal (coming from Unity) and I have been observing some strange behavior with what Actors/Components can reference other Actors/Components in the scene vs which can only reference ones in the content browser.

For example, I have a custom Actor class with publicly exposed references to an Actor blueprint class (named Reel) and a publicly exposed reference to an Actor Sequence Component (named Sequence). The Reel variable wants an Actor in scene. The Sequence wants an Actor Sequence Component in the Content Browser (but I don’t even understand how it could get such a reference as it has to be attached to an Actor).

Can anyone clear this confusion up and point to a place that explains this phenomenon?