Here's what Zuckerberg actually did do:
Fearing that his neighbors would eventually sell their house and one of the selling points would be, Hey! We live next to Mark Zuckerberg!, Mark went to all the houses beside him and behind him (the entire block) and bought each house from the current owners. He paid an astronomical sum of money, $30mil, for four houses.
He wants to control who lives around him and keep out prying eyes and perhaps in the future tear down those houses and extend his property lines.
In the meantime, after buying the homes he is now leasing back to the sellers so they can stay in their homes.