Not sure that they've got the effect of the copper foil shielding quite right in that analysis. 150pF is only about 3 feet/1m of typical guitar cable, and I really can't see that small amount bringing the resonant peak down from 3.7kHz to 3.2kHz. The resonant peak figure is given without a cable attached (as no-one knows what cable type and length you are using). That 500Hz drop would indicate that adding an 18 foot cable at 80pF per foot would drop the resonant peak right down and the pickups would sound really dull (which is not the case), so I can't see that being correct.

I'd expect they've got a decimal point in the wrong place or confused picofarads with nanofarads, or measured the extra capacitance value incorrectly or something similar.

It will certainly have an effect, but for that given capacitance figure, I don't think it can be anywhere near as big as suggested.