Forgive me if I'm a bit skeptical of his words. He might not have *all* of the coins or maybe they aren't "just sitting around", but he might have a lot of them.
He's offered to pay full interest on these accounts. If he's got any coins at all it's in his best interest to pay off any liabilities as soon as possible instead of letting the interest accumulate. So, either he doesn't have the coins or he's willingly letting people quickly destroy his profits.