Not sure. But if you think about it where else would it put the fuel? It's a small airplane and the whole front of the fuselage is taken up by the crew, avionics, and engine. So you have only two empty places to put the fuel, tail and wings, if you put it in the tail you will screw up the CG and the plane will be unflyable, this means the only place to put the fuel is in the wing(s).
Also when your sitting in the cockpit and turn you head to either wing you will see this stick like thing sticking vertically down from the wing, I believe those are the fuel quantity indicator.
Are you sure you saw a real one not a replica?
I've been looking at some of it's pictures and those things looks pretty thick.
