Not really.

Even since the idea of the East London Line first surfaced (around 20 years ago) it has always been assumed that it would be part of the BR/National Rail network. Indeed when the Thames Tunnel was refurbished the structure gauge assumed it was a Networker.

When TfL was formed the proposal was given to TfL London Rail (which monitors National Rail services in Greater London). Therefore, it was totally natural that the extended East London Line would become part of London Overground rather than London Underground.

There are also umpteen technical reasons as to why it would have been very difficult for the line to be part of LUL and still run to Clapham Junction, Crystal Palace and West Croydon (and New Cross).

It should be remembered that LOROL runs a concession not a franchise. That means that LOROL have many KPIs (which are specified by TfL London Rail) that they must meet. The revenue risk is held by TfL London Rail not with LOROL.