The First Amendment doesn't mention anything about secrets, that's not what this is about. If I sell you a stolen item, and you know it is stolen, you're guilty of a crime. If you later try to sell or move those goods, that's a more severe crime, fencing. In this case the reporter is obtaining "stolen" information and passing it along, it's exactly the "fencing" of information.

I'm aware this practice has been going on for decades, people leaking private and/or classified information, often illegally. But it's like money laundering, just "info" laundering through an "unnamed source," and it feels pretty sleazy.

https://en.wikipedia.org/wiki/Possession_of_stolen_goods