He didn't say they were wearing mud and leaves for clothes, he just said that if they were, to an Aurvandilan's eyes we wouldn't notice the difference. The entire description was hyperbole to contrast the Barcan's to the insane level of opulence in Aurvandil civilisation.
So he didn't say they are wearing mud and leaves for clothes but thats what he feels like they are wearing, which is even more insulting.
