The only moment Kylo and Luke both perceive differently (and both incorrectly) in the flashbacks is basically who turned their lightsaber on first. With this change of only Kylo killing everyone, his reaction to perceiving Luke there as a crazed lunatic trying to murder him is better warranted, almost. Kylo was terrified and alone; perhaps now all of the propaganda Snoke was feeding him just finally rang true for Ben and he had a massive freakout and killed everyone. I still like that better than some random students leaving, I don’t really see the point of even mentioning that detail. Not just because it doesn’t come back to mean anything later, but because it’s better to showcase Kylo did all this by himself. All because of how he saw Luke, and how turned his heart was. At least that’s how I’m seeing it right now, I could change my mind later, maybe.