What doesn't gel with the RBS/jackstall theory (they are so similar it's difficult to tell them apart) is the low Nr horn - that sort of disc loading produces high Nr not low.
The same horn also provides aural warning of low or high main rotor speed, that is, when the rotor is between 250 and 360 rpm (continuous sound) and above 410 rpm (intermittent sound).
Have another listen - sounds like it worked as advertised.