I know what you did, because the same thing happened to one of my friend.
You just use the "erase all data & settings" feature on a jailbroken device.
To make simple,the jailbreak moves crucial files on the device, to make space on the system partition (where the cydia apps install). The erase function deletes theses files, because they shouldn't be here. The device cannot boot anymore, restore in itunes is the only solution.
Now maybe you never jailbroke your ipad, in that case restore is again the solution, but its good to prevent people to use that button on a jailbroken device.