The same Page also contained this quote further down:
Spend in currencies in your account: Free
So I assume this applies.
It is probably more of an unintended use (then again these days everything is a hack).
This seems to be the most likely option. I mean this is relatively tame, have you seen US Credit-cards and their insane cashback and rewards programs (there were like some 2-5% ones) that are probably mostly paid by other users paying 20+% interest because they have no Idea how to deal with money?