The CSD Unit is normally integral with the generator; therefore, the disconnect is between the CSD and the engine gearbox; not between the CSD and the Generator. Therefore, it's only the CSD that can be disconnected from the engine gearbox.

The disconnect is there for the purpose of isolating a hydromechanical unit i.e. it might either be leaking oil, overheating, or causing the load sharing system to do oddball things. If you operate the disconnect, it will dump the generator via the CSD i.e. the rotational input from the engine gearbox is removed and resolves the oil leak/problem.