Well it’s not like TRoS bothered to contradict that. Didn’t build up on it either, but it’s easy to headcannon that as the backstory for the KoR if somebody wants to. Better than nothing, I guess (which is what we got in TRoS).

Personally I haven’t checked the ancillary material, but I like the idea this line conveyed - that it wasn’t all sunshine and rainbows with Luke’s would-be Jedi students besides Ben, to the point that some would take Ben’s side in the ensuing mess and confusion. Whether they became the KoR or not, it makes sense that Ben might have convinced some students of his side of the story, or maybe there was already some division before that fateful night and that was just the turning point. Either way I think it’s great and gives it a lot of nuance in very few words, the alternative of “Everything was perfect 'til Ben single-handedly destroyed it” is a lot less interesting.