It is fairly rare for stocks to be so heavily shorted.

It doesn't necessarily take a bunch of people to make the price move up, but it does take a lot of money, enough to capture most of the floating shares of stock. And in particular these folks banded together to use call options to amplify their money (and risk) as they purchased stock to drive the price up.

The only thing new is that rather than a few dozen wealthy people coordinating behind closed doors to use a ton of money to cause the short squeeze, it was a ton of small time investors coordinating in public, plus a bunch of others hopping on board when they saw what was going on.