Yeah I don’t like the idea that a “frightened boy” proceeded to slaughter all of the other, innocent, students. Specially if he believed he attacked Luke in self defense. I’m sure that’s why Rian implied there was more to that story, even though we only hear Luke’s side of it. Hal trimmed the scenes of Anakin killing younglings precisely to avoid such a drastic turn and here he’d be doing the opposite. I always pictured something like the Craster’s Keep mutiny from GoT, where right after Jeor Mormont dies everyone has to pick a side and those who refuse to mutiny are killed by the mutineers.

And well, a lot of people assumed they were the KoR based on Luke’s words alone, simply because they follow Ren as their Leader, yeah they don’t use lightsabers and don’t show mastery of the Force, but they were just students and we don’t know for how long they trained. Ben had the “raw strenght” and the drive to be like his grandfather, which would be why he’d be picked as the Leader, while the rest aren’t really trying to be Sith. All headcannon, of course, and you can still take the “canon” answer if you prefer. Either way I think that line has a lot of value.