whos "they" and what is the software looking for ?
Betting site operators. Software looks at large bets in obscure markets, it gets cross referenced with user betting history and previous bet size and then it gets flagged (new account would get flagged too)
Betting site operator also should have had a max bet limit which wouldn't have allowed such large bets to be placed, and automatically sends it to a human to do a risk assessment. But most sites are barely legal so they don't bother with that stuff. It's only when they take a hit that they start caring.