Don't be silly, you can't possibly be responsible for breaking an embargo you weren't subject to or informed about.
Responsibility may include vetting your sources - is this person competent and dutiful, to actually know there's no embargo? - and researching the situation, and thinking several moves ahead, and other stuff.
Reality is that everyone has to make decisions in finite time, using the resources they actually have.
And I'd put a whole lot more responsibility further up that chain of contacts. And question how many other people they might have blabbered to.
That's fair. For clarity: I take responsibility for posting on HN, without knowing the facts.