About a year ago, Google started having new Nexus devices from the Google Play ship pre-configured to your Google Account before they leave the factory. (It makes the box-opening more magical -- turn it on and GMail works, as opposed to turn it on and then have to type in your email address and password.) So if the new device was one of these, presumably someone or something in China turned it on and did some voodoo magic to pre-install your account on the device before it went into a box to be shipped to you.