If you (like one of reader comments on the NYT piece itself) are asking about what law is involved with this, the answer is "none". Nor, if you think about it a bit, could there be in the USA given the First Amendment. Once you voluntarily share facts and opinions with a 3rd party that information is theirs and they may legally disclose it as they wish. Even if there was a valid, written contract around it that would still be a matter of civil, not criminal, penalties and further itself subject to abrogation by public interest arguments.
Whistleblower laws deal with power and retaliation against a discloser by organizational superiors and (in some instances and locations) the state. They are not about "journalists" (which isn't a special category) but about protecting the release of information in the public interest, and apply for everyone. They're not for recourse against reporting or revelation by independent parties though (in fact that'd be directly against the point of them).
So basically what it comes down to is honor, reputation and future dynamics. It's about soft power human relations, with everything that comes with that. Obviously a reporter that develops a reputation for betraying sources will be unlikely to ever again get any sources, and the same for a larger news organization. Given the competitive nature of reporting, a news organization whose well of tips and sources dried up would suffer heavily for it, if not collapse entirely. Additionally, it's rare that critical off the record/background/deep background information is an end by itself. Rather, it's a jumping off point for investigation and corroboration by public sources and those willing to go on the record, and that is then what serves as the real core of the story. It is often the case that something critical is hidden more in the vast sea of noise and other information rather then through any particularly deep level of protection, so being pointed in the right direction and having investigators start asking questions and digging is more then enough.
It's a complex dance of motivations on each side, but over time the equilibrium has generally ended up somewhat around what this article discusses in terms of ethics. Not just pure self-interest but even idealistic goals considered long term and simple morality/empathy tend to drive a respect towards keeping promises. However even then it's never 100% certain, and it's not just the occasional genuine ethical breach or scumbag either. It's conceivable even the most scrupulous reporter could come across something so important and time sensitive that they'd decide burning their career and other lives would be a price worth paying and then just report it regardless. Conversely sources by definition are also always taking some risk by not keeping something to themselves, and will have their own sets of motivations and calculations about whether it's worth it or not.
Whistleblower laws deal with power and retaliation against a discloser by organizational superiors and (in some instances and locations) the state. They are not about "journalists" (which isn't a special category) but about protecting the release of information in the public interest, and apply for everyone. They're not for recourse against reporting or revelation by independent parties though (in fact that'd be directly against the point of them).
So basically what it comes down to is honor, reputation and future dynamics. It's about soft power human relations, with everything that comes with that. Obviously a reporter that develops a reputation for betraying sources will be unlikely to ever again get any sources, and the same for a larger news organization. Given the competitive nature of reporting, a news organization whose well of tips and sources dried up would suffer heavily for it, if not collapse entirely. Additionally, it's rare that critical off the record/background/deep background information is an end by itself. Rather, it's a jumping off point for investigation and corroboration by public sources and those willing to go on the record, and that is then what serves as the real core of the story. It is often the case that something critical is hidden more in the vast sea of noise and other information rather then through any particularly deep level of protection, so being pointed in the right direction and having investigators start asking questions and digging is more then enough.
It's a complex dance of motivations on each side, but over time the equilibrium has generally ended up somewhat around what this article discusses in terms of ethics. Not just pure self-interest but even idealistic goals considered long term and simple morality/empathy tend to drive a respect towards keeping promises. However even then it's never 100% certain, and it's not just the occasional genuine ethical breach or scumbag either. It's conceivable even the most scrupulous reporter could come across something so important and time sensitive that they'd decide burning their career and other lives would be a price worth paying and then just report it regardless. Conversely sources by definition are also always taking some risk by not keeping something to themselves, and will have their own sets of motivations and calculations about whether it's worth it or not.