A little caution is advised when lapping backmarkers. You braked about where you should for a normal lap, or if Knuckles had actually let Harabla and you pass (this is key, Knuckles clearly caused it).
When you saw that Knuckles was late on the brakes it was almost too late (you were already braking), but it would be smart to not be aiming your car at the site of the incident. By the time the incident happened between Knuckles and Harabla there was nothing you could do.
The incident is definitely NOT your fault, but even so it's better to be smart about passing backmarkers then be a victim of them.