When you review moves and have the standard settings applied you often have to overstudy a couple of moves. Let's look at an example:

After learning a variation you wait for 4 hours after which all of the moves become due for review. At this point, all moves are at level 1. When you do the review session you play all moves correctly except for one. This means that all correct moves advance to the next level (level 2) and will only be due after another 24 hours, but the incorrect move falls back to level 1 and is due for review after 4 hours.

When you return after 4 hours, but before 24 hours have passed, there will be one move that's due for review, but during the reviewing session, you will play all moves in this variation. The 40 points you score for the move that is due will count towards the global leaderboard. You will also score points when you overstudy the other moves in the variation, but they will only count towards the course leaderboard. This is why you have more points on the course leaderboard than overall.

When you set 'Review' to 'Randomized' in the course options you will only review moves that are due so that there is no overstudy, but you will play moves from random positions and won't have as much context.