There is a suggestion that the loan was only a way to reduce the amount of money we paid, Anderlecht apparently wanted a lot more from us (~4m) than they did from Olympiacus (~0.5m).
So we let them buy him on the cheap and we've got a set buyout fee if we want him that will cover their outlay plus some additional cash (~1m), and if we don't they still have a young player for little money.
The figures are ballpark, they are somewhere in the thread if you are interested but it is all speculation anyway, nothing confirmed by the clubs.