I think we have a chicken and egg problem here. The period of D&D's most rapid growth also was the period when the D&D scare first began, but like you, I don't find correlation here to indicate causation. It's just as easy - and in my opinion easier - to argue that the scare is being fed by D&D's rapid growth.
I think there's a problem of assuming that one strictly caused the other. I think it is just as easy, and in fact more reasonable, to assume there was a synergistic effect. Nature loves feedback loops.
D&D appears, some folks misunderstand, get scared, make noise. That raises visibility of D&D, more people buy it. Due to a couple of very visible events, the scared people get more scared, make more noise, and that continues to raise visibility, and visibility drives yet more sales.
The order of operations does not matter so much in a feedback loop - which comes first is academic. If you lack either element, the whole thing doesn't go nearly as far.