Theoretically, Scrum is a way to say 'work on this, because it's what aligns with the organization'. But, of course, whether it really does or not depends on who is implementing it and how.
How does Scrum reward the engineer, in a way that it does it better, and more profoundly, than other methodologies?
As the author noted, Scrum solves this problem by making number of story points completed the primary tool for a team to measure its productivity. If the cool-sounding project isn't important enough to take other items out of the sprint, there's no way to offer a post-hoc justification for doing it anyway. It has no story points, so work on it is considered non-productive.