I'm not sure specifically as I haven't read it in detail. But generally, it could be about a bet or wager that actually happened in real life, perhaps involving people, events, and the consequences of that wager.
I'm not sure specifically which 'the wager true story' you're referring to. There could be many stories with that name. It might be about a bet or wager that had real - life consequences, perhaps in a historical event, a personal anecdote, or in a specific field like sports or business.