It's not clear from the report whether there was continuity of rotation through to the mast.
I can't remember how you shut down a 300. I expect its to pull the mixture. He'd have to do that if rolling the throttle had no effect.
He may have "stopped" the engine and started the auto when the rotor rpm dropped out of the green. It might have been impossible to get it back once that happened. Especially with no power.
I don't think I'd have been at 950 feet when that was happening. If you can be at 950, you can be at 5 feet hovering, or no?
Good excerpt here on low rotor rpm from AOPA...
Of all helicopters, light, piston-engine types get into low-rotor rpm during normal flight most often. Most turbine helicopters have fuel governing systems that normally do a good job of maintaining engine and rotor rpm, which reduces the chance of rotor rpm slipping below the normal level. If the pilot of a light, piston-engine helicopter lets low-rotor rpm develop, merely opening the throttle may not produce enough engine power to overcome the rapidly rising drag on the rotor blades. If the helicopter is close to the ground, lowering the collective may be the last thing on a pilot's mind, but simultaneously lowering the collective and applying full throttle is the only sure way to recover the lost rotor rpm.
If the helicopter is hovering relatively close to a surface not suitable for landing, a pilot can sometimes recover lost rotor rpm by "milking" the collective. The pilot maintains full throttle and repeatedly lowers the collective using small movements. This reduces the angle of attack of the rotor blades while preventing the helicopter from hitting the surface. Milking the collective can be a scary business, but you have no alternative, and this can often be enough to persuade the rotor rpm to return to the green arc.
Good judgment comes from experience. Experience often comes from bad judgment.