so i mean:

say there is a number x (lets set this to 1 million, but i dont know the exact number, im just guessing)
if you bet 1 million satoshis in the multiply game, freebitco wins 5% (house edge) ON AVERAGE. That would be 50,000 satoshis loss for you.
from those 50,000 satoshis they could give you back maybe 5,000 (again, just guessing) through this bonus. so they would activate your bonus until you have collected 5,000 satoshis. then your bonus would drop, until you play the multiply game again.