I don’t know. It looks like GW2Efficiency isn’t completely accurate with their counts, as it gives duplicate Personal Story Achievement Points (it shows giving you credit for 10 Personal Story Mastery Points, instead of the maximum eight) that we know don’t count. Maybe it’s counting something else inaccurately, as well.
You could try counting the Mastery Points in the in-game Achievements panels, and see what that adds up to.
Good luck.