they are a BIT smarter than all of us combined and have more "tools" to get the best price...
again you think the 500k buy was a buy placed with Etrade or soemthing and now they are done buying. What makes you think this was the 1st and only buy?
maybe they bought yesterday, maybe Monday, maybe last week, maybe 2 weeks ago... etc etc
maybe this is the 2nd buy, 20th buy or 200th buy
you have no idea and we have no idea