"you got Kilo" was an inadvertent set-up call that the controller added to the mix, during a critical phase of flight, the landing and rollout, it is still requiring timely input to the aircraft control from the flight crew. The crew being familiar with HNL and requiring to do route quals even if not, would have been planning on a roll through to the end, that is what the charts give in the notes. That would likely have been the briefing and the intent up to the point that Kilo was mentioned by ATC. Immediately thereafter, the crew in the best intentions would be altering their mental model to determine if Kilo was an alternative, and would be biased towards taking action to make that happen. The time available to recall that it requires approval by ATC to exit for the large aircraft off 4R is limited.
With the best of intent, a non standard phrase in a critical time can have unintended consequences. One wonders why Kilo got a mention if the controller still had the Caravan in his mind, it being on short finals to 4L and otherwise impacted by any expeditious efforts for the traffic on 4R.
Would be interested in knowing the wind direction, as it would seem that separation was awfully cavalier for a caravan behind a heavy.