Observe que a borda de um sabre de luz nem sempre precisa cortar tudo o que toca. O poder é ajustável.
Por exemplo, sabres de luz de treinamento geralmente não decapitam nem desmembram pessoas:
Training lightsabers aka Youngling lightsabers were lightsabers of limited power—and thus limited danger—that were used for lightsaber practice. Training lightsabers were most often used by Jedi younglings[1] before they underwent the Gathering[3] and built a weapon of their own.[1] It was also possible for normal lightsabers to be tuned down so they could be used in this fashion.
A dupla barbada tinha maçanetas nos sabres para fazer o ajuste:
The blade power adjustment knob was a small knob located on the hilt of a lightsaber that could be used to make the weapon's energy blade more or less powerful, to meet the need of the current circumstances. Qui-Gon Jinn's and Anakin Skywalker's lightsaber had one of these.
Quem sabe, talvez o sabre de Kylo Ren estivesse com pouca energia, ou talvez ele tenha reduzido a energia (voluntariamente ou por acidente). Mais provavelmente Robert está certo e o sujeito que recebeu o golpe não foi tocado pela lâmina maior do sabre de Kylo.