How do you know? Skimming through his post history it looks like he is nothing more sinister than an investor. And with the volume that has been traded on coinmarket it seems like whatever coins that had been premined have already passed hands. I wouldn't put it past him to have tens of thousands of coins, but I believe he put the money and investment in and now wants to make something of it. No harm there.
550000 premine + 30min headstart to the dev's friend's pool.
Remember that before you decide to get into this coin guys.
https://www.coinmarket.io/market/RPDBTC
The volume just isn't there to assume that all the premine + early start coins were sold already.
Don't take my word for it.
The volume of the past 24 hours has been more than a third of the marketcap (and it has almost doubled in the past 24 hours so the amount of coins that refers to is much more than a third). And that is only after the crash. Before and during the crash saw even higher volumes.