The Mystery Spins buy was not cheap.
At C$10,000, Xposed needed a strong feature just to break even. With five spins remaining, the running total sat at C$10,668, so the bonus had already nudged into profit.
That could easily have been the whole story.
Instead, the next spin delivered C$256,000.
That is why the bonus-buy cost matters here. The 15,843.60x multiplier is calculated from the C$20 base bet, but the actual amount Xposed put at risk to enter the feature was C$10,000.
Seen that way, the result is still huge. A C$10,000 buy became C$316,872, with one spin responsible for most of the payout.