King Size Capacity is partly a marketing term, and may be partly features if the machine has a Triple Action agitator on which the auger is spring-loaded to lift itself slightly upwards and press down on the load for helping promote rollover. The effect during agitation doesn't trigger unless the load is very large to provide enough resistance.
You can determine if it's a Triple Action agitator by pulling upwards on the auger to feel the spring resistance. Some models have Triple Action Agitator descriptive text on the agitator cap.
This video on how to remove/replace the auger shows the spring mechanism.
This video (which is not mine) shows the vertical "triple" action with a set of king-size sheets and a king-size blanket. Watch closely, it's subtle. Easier to see at full-screen on a computer monitor than on a little phone. Many people probably would say the machine is overloaded but it's not.