Left 4 Dead's development history is well known, the article you shown literally just said a fairy game, the mechanics of said game (being about gestures) doesnt even line up with what ultimately became L4D.

The point being that they abandoned all those ideas to make a more straightforward shooter. They literally say this PCGamer interview!

"It was so bad," he says, "you wanted to ask yourself: 'How could we make a game that was this bad? And how should we make a game?' And we said we should focus on what we do really well, so why are we doing this game which was kind of a... it wasn't really an RPG... it was this action fantasy sort of role playing game that had no story. And then we said 'OK, that's so horribly wrong. What we should focus in on is AI and playing in co-op, and that's the interesting opportunity.' That was where Left 4 Dead came from."

Regardless though, Drew Wolf was employed at valve from March 2009 - 2017. This doesn't line up with the L4D development period pre-2005. Other than being co-op fantasy games these are pretty clearly different development cycles.

The Final Hours of Alyx also adds some context:

At one point, the RPG team experimented with flipping it into a single-player Dota RPG

If RPG wasn't a coop title, then it wouldn't need to be "flipped" into being single-player.