Gamblers who can win multiple times or large sums of money will become greedy because they will see that the opportunity to get more money has come and will have to use it to win again. But some gamblers can control themselves and know that their time has come to a stop and they obey it because they know that victory is not always on their side. As long as they can control their emotions, they will be able to master gambling and will not become greedy because they know that gambling is entertainment that can cause two things: winning and losing.
There is a huge chance for a gambler on a winning streak to get greedy but if he is disciplined enough and keeps on the planned activity, he can avoid being greedy. Though I agree that most of the time gamblers that has no dedicated plan for gambling often got hooked on the winnings and get greedy until they lost everything. But OP's story is different, the person in the story managed to stop and get away with the winning with motivation in hand which solves the problem of his company later.
It is very difficult to stay calm when you are winning,yesterday I was playing a slot machine and I was just playing little money and didn't expect a big win but the slot machine kept giving me big wins on regular basis,I got from 69 dollars to 1200 but only withdrew 500 in the end because I thought to myself why not risk 700 dollars by playing with a higher bet and hopefully to hit the maximum pay line.I didn't and lost them really soon but I ended up with a 400 dollar profit in the end.I could not stop at 1200 because I thought why not go for that big prize and that is what hit most gamblers.