Okay, this is a test:
Sails are down, you are drifting with the wind and current, the autopilot is engaged, the engine is running, the transmission is in neutral, it is nighttime, youre having dinner in the cockpit with cockpit lights on. What navigation lights do you show?
IMHO, you are technically "underway". As an underway vessel you are required to follow the ROR.
As to whether you show the lights of a sailboat or those of a power boat, I would suggest that even though you're engine is not engaged, it is running and you should probably display your steaming light.
Technically, you are not sailing. To claim stand-on status over a power driven vessel you'd have to be " under sail" . In reality, you are no different than a power boat that is drift fishing.
You should probably not have your cockpit lights on, since they are not navigation lights. I understand that in practice, vessels like party boats, fishing boat, cruise ships, work boats etc often have more lights on deck than navigation lights... I think as long as the lights can't be confused as Navigation lights...you'd be ok though. But, I think your steaming light should be on.