The decentralized nature of bitcoin makes it impossible to by a pyramid scam. However, it could be one of the most well orchestrated guerrilla marketing stunts in history.

Guerrilla marketing is when the person trying to sell the product goes undercover as a user and then tells people that they should buy it. So in the case of bitcoin, maybe a bunch of people got together, created a concept, filled their wallets with the coins at a dollar a pop, and then set off to work. They spread the hype around the internet and after several months/years of hard work, boom! It took off. It's not hard to imagine, and it's not necessarily a scam, because they weren't deliberately taking money from anyone.