I suspect eligibility is, in practice, determined by "MDE identity". If that identity (a) owns a qualifying membership and (b) has a stay directly booked through MS, that's good enough, though I suspect it is not the intention of DVD.
Furthermore, I can imagine DVD not wanting to go to great lengths to "fix" it---it's a subtle enough difference that there is no real reason to tick off Members who might otherwise still eventually buy direct (unrestricted) points.
Yesh because for MM, all that is required is that you are eligible, DVc Y, and have a reservation booked via your membership.
So, it doesn’t matter which one you used. Now, they could change that in the future to state that reservations must also be booked in a membership that is eligible, but for now, it doesn’t matter.