I doubt the amount because guys like TheKoziTwo were involved earlier than Risto. He created the first Monero exchange and was in a much better position to acquire a such a large amount, but IIRC he indicated he had less than half of that. Buying 700k coins during that time on the open market doesn't seem possible without a massive price run (which never really happened. USD high post Mintpal pump was like $3). And I doubt he was making any significant OTC purchases either. The community wasn't that big at the time.
EDIT: back to speculation. If XMR breaks $110 this week we will be on target to $425 by December.
I'm curious how you arrive at that figure. Has it really been pulled from somewhere the sun don't shine or is there a rational basis for it?
It's a very rough assumption based on past market runs. Monero went from about $3 to $15 last year (5x increase), from about $12 (March 10th) to a high of $60 earlier this year (5x increase), then from $30 on July 16th to $150 (5x increase). So if our last strong support was at $85 then I'm predicting our next 5x run will bring us to $425, which should happen no later than December 15th (45 day interval).
EDIT: Also, the Nov. 1st 2016 run from $4 to $18.5
almost fits the pattern.