Jokes aside. My guess would be that it is highly unlikely a half decent secret service would use such a method to spread a virus or a trojan. On the other hand, I would also guess that no serious journalist will contemplate using a free device provided by a rogue nation just in case.
I disagree. While tech-minded journalists may be aware of the risks of untrusted USB devices, the same cannot be expected of everyone; even if they know that USB drives are potentially dangerous (already a crapshoot, even in some tech-related jobs), people unfamiliar with computers may not realize that the same risks apply to all USB-powered devices.
It's possible he put the date on which he plans to more formally publish or present it.