Orientation is now a convention adopted as a consequence of US LHD unfluence as per your theory, eventually becoming de rigueur through US virtual total domination of airliner manufacturing industry after WWII.

Not absolutely sure why the US didn't adopt the same parochiality with relocating heli controls & orientation, but helis fly command from the right because that's the way the controls are orientated if used in the natural sense. eg: throttle/collective controlled by left hand.

With few exceptions single pilot 'stick' aircraft fixed wing or rotary have the controls orientated to be flown with the command pilot controlling the primary flight controls with his right hand (and feet), throttle with the left. A contemporary exception possibly being some airbus industry FBW types with the 'stick' such that it is, located on the left possibly to keep with contemporary airliner convention and implementation ergonomic?

Just like in Africa, they drive in the 'middle' of the road in Russia...where roads actually exist.