Assuming it hits, Khan was right in doing what he did.

In combat, you won't find anyone whose going to sit there and let you do what you want and react after the fact.

Khan ran when LeeRoy did, and by the looks of it reached him before he reached the door using Whatsherfaces speed to do it. LeeRoy now has to stop his actions(since he wouldn't make it to the door without first avoiding a blade to the back, or being sliced in two), hence the interrupt.

He stopped the actions from happening, by stopping LeeRoy from reaching the door. 

As an example, if you say you threw ten jabs at opponent B, and he stopped you at 4, you don't continue to send them. 6 out of those 10 are now null and void.