I think it's relevant in the sense that it shows if you're building a simple app, there's a lot of overhead.
It doesn't claim that you're going to get that overhead for every time you instance a button. I don't see how anyone would think that.
I think the comparison works fairly well. It should be clear to everyone that it compares apples and oranges, since it's two different kind of apps it's comparing. So it makes you think. If they just compared the size of the framework itself, or a single button vs a single button, you may think "oh but as soon as you add any kind of complicated code, there will probably be so much boilerplate with Nue that it'll end up being bigger"..
It's still a neat toolkit, since not every website needs a big framework - but comparing runtime sizes is like choosing C over C++ because a `int main() { printf("Hello World\n"); }` binary is smaller.