Sounds to me like what you have there is a poor man's transfer switch.
Many modern motor homes with generators have a device called an automatic transfer switch.. What it does is monitor the generator and if it's running, it "Transfers" power loads from the SHORE POWER inlet to the Generator (make sure you turn them off first or turn off shore power for 2 minutes before starting genny)
But some older rigs (And I suspect some modern ones too) have a "Poor Man's" transfer
The generator feeds the outlet (Female connector) and to transfer from SHORE to Generator power.. You physically transfer the plug from the shore cord to the outlet you described.