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.
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.