The bet was close to even odds. Also since this was a one time bet, with the downside of (probably) him never betting again, even if it payed out 10x the money

The bet was close to even odds. Also since this was a one time bet, with the downside of (probably) him never betting again, even if it payed out 10x the money he bet, you would still want to be pretty sure you were right -- and not just "making the right bet" since the downsides far outweigh the upsides. This isn't "on a long enough timeline" bet, it is a "I need to be correct this time" bet.