He did not complete the wagering requirement, we can't simply say statistically while involve in gambling. He may win or lose the entire balance before completing the requirement.

Most casino did this, player could end up cancelling the entire balance after part of wagering requirement has been done, except most of them are clearly written in the terms and conditions that Real Money will be use first before the bonus balance is used. They make it clear, but Duckdice didn't. Duckdice use the same algorithm, thus they should actually write in this way (Main account funds will be used before any bonus funds, an example took from FortuneJack), real balance will be locked while bonus is active is the only reason that misleading the players.

Duckdice didn't make it clear in the terms and conditions, that was their fault, BUT, when cancelling a bonus, there will be a popup box showing up how much balance will be left in your account after cancelling your bonus, if player read before clicking any Cancel | Button, they should know!

FOR EVERYONE INFORMATION
Here is what happening when you are canceling your bonus:

First screen example:



Second confirmation screen example:

Even if they are clicking too fast, there will be a second windows to ask for the confirmation, player should read! This was the player fault. Again, player should READ CLEARLY before performing these kind of action, just taking a few minutes to read, easy task, it is the player responsibility. You cannot simply ask for a refund just because of your own mistake. In this case, cancelling the bonus without reading clearly was the player fault, and Duckdice still refund his deposit of 2BTC, fair enough.