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We, on HN, all have an idea of the tech behind this, but to the user, it is still perceived as an undo action, and that's what I believe the point of the author was.

It's not job cancellation, your view is such that unless you undo, that's reality (you can confirm this by browsing in a separate window, your non-undone actions have taken place).

What Google is doing is (at least for deletes on mails) is equivalent to a database transaction rollback. So they have a tiny (likely 1-entry) transaction log that they keep per user, and if the user desires, they can use it to fully reverse any operation that is undoable aka reversible.

I suppose it works different for email sends you can undo - in that case it is job cancellation.

Gmail can't, but Exchange and Skype can (and do).