I'm just wondering what's the difference between "Remote controller" and the "Flight Controller". Thought they were one in the same but I see they have different serial numbers.

They are different, the flight controller is the Main Controller which is inside the drone. As for the remoter controller, here is a pic of the P4P remote controllers for your reference only.

See Diana's explanation above. This may help as well. The Remote Controller sends the commands to the flight controller. The flight controller can also be uploaded with data such as coordinates and commands from an app such as a mapping program. That is how your Aircraft will fly a pattern and take photos for a file to be stitched together for a map. Hope this helps.

Thank you it all makes sense now.

thanks for this explanation, it was very helpfull for me even after this years