Like paul said, with the smaller arrow diametars used by young archers, it can be difficult to tune a prong rest no matter what style fletching you use. also since the young archer is probably going to be using a fixed head he's going to need every advantage he can get to get that arrow to turn quickly.

I have always used straight fletch with fixed heads and they shoot just fine.

No, he didn't need a new rest and refletched arrows to shoot broadheads. It is though hard to say how the conversation actually went. Either way the boy's had some schooling. Not a bad thing.