Two things may be coming into play here:
1. Friend is not being truthful
2. Friend is on a lucky streak
Lots of betting systems have very poor risk reward metrics. For example you risk $1000 to make $50 but your “winning” percentage is relatively high…maybe you win 95% of the time but your winners are small but that 5% of the time when you lose, you lose all of your winners plus some of your own money. The thing is you can go a long time without losing but if you have a few losers in a row it can get out of hand really really fast. Just some stuff to think about maybe.