Those two statements do contradict each other. According to my own quick analysis, this library uses truly native controls on Mac and GTK+, but its own windowless implementations on Windows. The Windows control implementations use uxtheme so they look more or less native, but that's not "native controls" as far as I'm concerned.
If better skinning is the intended advantage, then it's apparently not implemented yet. I would also like to know the developer's reasoning, since using non-native controls makes it much harder to support accessibility, and this library hasn't yet addressed that.
I think it's easier to port your own drawing code from platform to platform. That's probably why Firefox and Chrome can be multi platform because their rendering code is the same.
Doing a cross platform UI library that uses native controls seems a lot of work.
