which can be interpreted as right after, or thematically after, or any number of ways ...

I would guess they probably mean thematically, that is, with some kind of rebalancing of the force.

If you look at it this way:

ANH: 2 Jedi, 2 Sith (Yoda, Obi & Vader, Sidious; or as balanced as it gets)
ESTB: 1 Jedi, 2 Sith (with Luke in training to bring the balance as 2nd Jedi)
ROTJ: 2 Jedi, 2 Sith (at the beginning), but only Luke at the end, with his mixed baggage and Anakin style uniform

You could make a case for Luke internally balancing the force, but how long does that last?

The next movie would have to address that, and then fill the void depending on which path he ends up favoring.