I suspect they've misunderstood how London line nomenclature works. They're suggesting names for various sections of track on the Overground network, in the same way that sections of the national network have distinct names, and trains run over multiple sections (eg no train runs the entire length of the B&H but terminates at either end).
This response has triggered a memory about the naming of routes in the UK, it might have been a very long time ago on here. In other countries, particularly the US, named lines are the norm, while in the UK it's much rarer. I can't remember the full details of the distant memory, but it was something like observing that if you boarded any given train at, say, Preston, you wouldn't necessarily know if you were on a Blackpool train, London train, Ormskirk train, etc., because we only have services, we don't have named lines.
A vague recollection mind.