Pirate is a genius.
1. The bet takes and pirate defaults: Van makes 5k
2. The bet takes and pirate doesn't default: van loses 5k
3. The bet doesn't take and van goes long: he makes over 8k
4. The bet doesn't take and van does nothing: he is even
So essentially taking this bet is the only way for van to lose money, and if he is wrong he limited his profit versus going long.
*applause*
If the pirate default is a 100% certainty, then betting on it is not a bad idea. Vandroiy is 100% certain, so this explains his actions.