Overstock is important player in RVN project, but if they don't lie about it - they own ~85 millions of RVN. That's only 5% of circulating supply.
They can not lie about it because they are listed at the stock exchange and providing false numbers to investors is a mortal sin.
Of course they are free to sell their coins after the announcement but this seems unlikely because of their heavy involvement providing funds and developers etc. Since last quarter they even increased their holdings.