Don't misunderstand, it's not that I'm really trying to defend google. This is to serve as a reality check and warning to those who don't understand the rules of employment. And I'm guessing the Engineer in question understood the risk full well.
I don't disagree with that either. I'm just saying that, if this is the company's choice of fireable offense if the company actually considers it normal to exercise the right to dismiss an employee (which they legally do have) for this sort of mistake, I'm glad I don't work there.
As I mentioned in another comment, I recently did something at work that you could spin in an equally sinister way, if you want. My company would be within its rights to fire me for it. My employer would be within its rights to fire me for sneezing at the wrong time, or even for no reason at all. I choose to continue working at this company because I trust that, despite their legal ability, they have no intention of actually doing so. If I ever lost that trust, I would leave.
(In fact, my employer and Google's also have very similar employment agreements about ownership of outside IP / personal open source, but I had reasons to trust my employer to act more reasonably than Google, which was part of why I chose my current employer when deciding about it and Google. In practice that trust has turned out to be well-placed, and there's now a thread on the front page about how Google loves to follow the letter of the employment agreement and arbitrarily deny IARC requests.)
If you could concisely and cogently explain why this change is a bad idea in an HN comment, surely someone can do that in response to the change, revert it, and move on. If it's SOP for Google to fire people who make well-intentioned changes that have the side effect of alert fatigue, then one, I don't want to work there, and two, I would expect to see a lot more firings.
And surely they could explain the problem, revert it, and move on without calling her into a conference room and grilling her about who else she's organizing with. That makes it seem like it's about the content of the notification, not the alert fatigue.