That's because the ferment took off and was really active and the pressure built up. You're lucky you didn't have a bottle bomb.

Fermenting things the way this article instructs is very dangerous and one of the dumbest things to do. Proper and SAFE fermenting requires an airlock so the CO2 can escape without letting in oxygen. An airlock is inexpensive (about $1-2). All you do is drill a hole in the lid, put in a rubber grommet, and put the airlock on with some water in it. You can buy them from any brew supply store. There's a company that has jars and lids all set up with airlocks but are a rip off for the prices they charge.

I know there are people who swear by this "open the jar daily" method, and may work for them. But it is dangerous.