Occasionally a player may have 2 or more bonuses active in their account.
If a game is eligible for both/all bonuses, then the gameplay will count towards the wagering requirement of the bonus that you began to play through first.
You can tell which bonus is the oldest by going into My Account >> Bonus History.
The bonus that the gameplay will count towards will be whichever bonus is active and at the top of the Bonus History page.