That reminds me of an old story where an owner of a well-known business gambled the remaining portion of their funds in hopes of avoiding bankruptcy and it paid off once their bets ended up winning.
I never see gambling as a bad activity unless you gives yourself up to it in controlling your emotions. So I think these two guys knew they were at the wrong side of it that is why they never wanted me to know they were into gambling.
If it's an idea expected to fail, they most likely thought you'd try to stop them, and maybe that's why they kept it a secret. It might've been a different story if he won, but still relying on luck, specifically through gambling, always backfires.