What if this guy with $10 billion suddenly starts buying Bitcoin?
Does this mean an insignificant drop of ca. 0.57%?
Circulating supply is irrelevant, most of it isn't "circulating". Only a small portion is traded each day. Trade volume is currently $7 billion per day.
Buying with dollars increases the price, selling Bitcoins lowers it. The market will always find an equilibrium, which makes speculating like this useless.