Apparently by a Spanish presentation that showed a slide with names of upcoming 3DS games at the end, including some not officially announced for a worldwide release. Here’s the slide in question:
As you can see Bravely Default and Professor Layton vs Ace Attorney are listed as being released in that year, along with quite a few Japan only titles.
However, it’s still just a rumour. And while it’s a plausible enough one (all the games shown are from well known series that would probably sell okay outside of Japan, and many have already been confirmed for a worldwide release), it’s also not exactly the hardest thing to fake, since anyone with an image editor could mock up a picture identical to the above.
But yes, looks like a potentially accurate 2013 3DS game line up. And hey, Project X Zone is listed!