While they could be drawn similarly to how Wang tiles are drawn, they definitely lack the aperiodicity property of Wang tiles. (Eg there are tiles with all four edges the same, hence you could tile the plain with nothing but that tile.) Of course the other distinction is that you only use each tile once in Carcassonne, unlike a set of Wang tiles.

It doesn't look like aperiodicity is a required property of Wang tiles. Just the cool ones. :)

I suppose you're right.