Seems clear to me that Marc’s point is that we are using the wrong term for what has long been held to be “polyphonic”. It should be “multiphonic”
It’s most likely beyond that point as a common parlance is defined by its usage(especially in the world of marketing!). Not always related to it’s historical use.
This hardly makes Marc wrong. His opinion on this, given how well researched it is, is probably the most correct-ish.