Contrary to popular belief in close quarter combat a knife is far more dangerous than a gun. A gun requires action on the part of the assailant while a knife can be dangerous with only reactionary movement. For example one of the key tenants of close quarter combat is explosive violence, basically when you go you go off. When you do the assailant has a small window of time to chose an action e.g. aim and pull the trigger. With a gun the slightest movement moves you out of trajectory which require a new action on the part of the assailant these calculations are not as fast as reaction time. Conversely with a knife it can be wielded in a reactionary fashion e.g I go to grab it the assailant flinches back and I get slashed. The weapon can be used without the assailant consciously choosing to do so.

Unfortunately the best (read safest) method for dealing with a knife telegraphs your intention and throws explosive violence out the window because the most assured way is to either pick up a longer instrument (bat, tire iron) or to take off an item of clothing to act as the item to trap the arm either of which let the assailant know what the score is.

Knowing this and reading that the gentleman still opted to use the element of surprise, gives some insight as to how confident this individual was with his abilities. The fact that he first used his feet to disarm the knife says that he analyzed the situation and decided that the element of surprise was more valuable than opting for a telegraphed safer method.