However, even if you just had a single 'sheet' curved aerofoil, it would still have a top and a bottom.
This is more a question of a curved aerofoil compared to a flat one, as most aerofoils have a flatter underside than top. Even concave ones.
I don't think it's bunkum. Try stripping the fabric off the top of one side and the bottom of the other and see which way the thing will roll, even with a concave underside.
A rotating cylinder yes, non rotating, like most wings, no. Different principle, slightly.