It's 2013, we have the internets, 24/7 news and no end of sources on everything related to politics of any country on the planet.
If something you don't know becomes vital to a project you're planning, you fire up Google every day for a few hours and learn what's going on. It's clear he didn't leak on a whim: he planned it over a certain period of time and, being a smart fellow, had all the time in the world to read up on the fine points of US international diplomacy, which would significantly narrow down his research pool on extradition systems.