Yes, it is.
It said they changed the concept of the Horde to be that, after they considered making playable Scourge for the undead faction.
They were originally envisioned as evil when the entire Horde was meant to be evil. When they changed the concept of the Horde, they also changed the concept of the undead.
Yes, before the concept of the Horde was changed.
In other words, the timeline goes like this:
- Plans for evil Horde with playable Scourge as the undead race.
- Release of Warcraft III.
- Realization that players enjoy playing heroic monsters.
- Redesign of the entire Horde to fit the new concept, including changing the undead race from playable Scourge to Forsaken.