5 coins from JUST that? He did next to nothing, he was just showing how it worked. If you think about it logically, there will be a bonus for clearing the board, and it multiplies and so on each new board you make it to.
I imagine this was confirmed when it was first revealed, "As you progress without hitting any voltorbs, the levels get harder" as quoted from Serebii's article on it. So you keep hitting multipliers, the more coins you get, progress as far as you can and quit when you think you can go no further.
EDIT: I'm gonna have to see how these multipliers actually do work, from what I can tell in the video where he won 5 coins, he achieved:
x1
x2
x2
So for level one the base value of a correct square is 1 coin, and it really cant stay the same way through other levels as it'd eliminate the point for multipliers and the incentive to continue going despite the risk.
So looking at what I'm predicting:
Consecutive board number = X
1 * X = X
2 * X
3 * X
Although a prediction, I'm confident this is the system they are using.