There are three roads a person can take. Light, Dark and Twilight. And that whole path choosing thing is pretty much only for Riku in CoM.
Here is the conversation between Riku and DiZ
Riku: What are you making me choose now?
DiZ: Will you take the road to light? Or the road to darkness?
Riku: Neither, I'm taking the middle path.
DiZ: The twilit road to nightfall?
Riku: No, the road to dawn.
Now we all know that the middle path is Twilight, or Twilit if you wanna call it that. But saying there's a difference in Twilight and Dawn is stupid. Dawn is Darkness to Light, hance why Riku called his Twilight path Dawn. Because he was going from Darkness to Light. Now Nightfall, or Dusk, would be Light to Darkness, meaning someone is pretty much using good powers for evil, as opposed to Riku using his powers of darkness for good.
There is only three paths Light, Dark and Twilight. It just so happens that two things can be classifed as Twilight, those who use Darkness for the good and those who use Light for bad. So Ansem wasn't wrong about the pathways. He just assumed that Riku would fall to Darkness again, but Riku reassured him that, that wasn't going to happen again, and he would use his darkness for good. It all makes sense when you play CoM and understand that Riku has just surpressed Xehanort's Heartless with his heart hoping that he won't take control of him, thus Riku falling to Darkness again, which worries DiZ.