I am having trouble understanding what the article is actually saying. Granted I have long forgotten most of my high school physics.
It sounds like the article is saying that if you break down a complex sound wave down into its individual single frequency components, and you add up the speed of all these individual single frequency components, then you have a theoretical speed of propagation that exceeds the speed of light.
Am I getting this correctly? My physics is a bit rusty here, but if you perform a fourier transform of any complex soundwave, you are going to end up with thousands (if not more) of individual frequency components. Multiply the speed of sound by however many individual frequencies you come up with, of course theoretically that number can exceed the speed of light.