What's the difference between a "runaway prop" and a "feathered prop"?
A "run away prop" is caused by a failure of the pitch control mechanism of a constant speed propeller.  Feathering turns the prop blade as close to 90 degrees to the wind as possible, minimizing the effects of the airstream.  This obviously reduces drag and is used when an engine is shut down.

A run away condition is created when the propeller malfunction causes the blade to move to the "fine" setting, which is used at slower air speeds.  It is the opposite of being feathered in that now the prop blades are much more angled to the wind as in a windmill.  The force of the airstream literally now turns the engine to excessive rpm.  The prop is at the wrong pitch for its airspeed, much like a truck dropping into low gear at highway speed.  The engine rpm redlines and causes overheating, while the drag of the improperly set prop slows the plane down.

Thankfully, the pilot was aware of the danger and was able to get away.