I have a 7 year old, and I think the parent is right. It would be
very hard to unwind the winning experience from the psyche of a kid. They'd be talking about it for months - maybe even years. My kid still talks about the run-of-the-mill soccer goal he scored three weeks ago.
Parent is dramatizing it, and one event probably wouldn't make _that_ much of a difference in life outcome, but I think there's a valuable lesson here. The dad was gambling.