90 HP on a moped? I don't think so. The same type of Honda I have (SS50) with a 153cc bigbore kit (max. available, 59mm bore with a 56mm stroke crank) will produce about 16 - 18 HP. His ped's probably a 2-stroke (an SS50 is a 4-stroke) so he's got 30% more power, that makes 23.4 HP. Than maybe he could find a supercharger (there's one available for my ped manufactured by Takegawa, costs $1200) wich will add about 80% power, that makes 42 HP. So it's possible to get a moped up to 40 HP, but it'll cost about $2000 in parts. Lets just say he really did install $2000 in high performance parts, he'll need a bit more than 300 cc's to produce 90HP and there is NO WAY in the world anyone can fit a 300 cc kit onto any kind of moped engine, they're simply too small for it.
I have by the way only once seen a Honda 4-stroke (It was a Dax ST50) with a supercharger on it, those things are incredibly expensive and incredibly hard to get and I have never heard of a supercharger for any other brand of moped.
By the way, I can't think of another French moped brand besides Motobecane and Peugot.
You know what? I think the old guy meant he had a moped with 90cc, not 90 Hp.