Exactly. He's using the wrong words to describe his point, which is that he doesn't think this particular mathematical language is useful. To someone who is flu

Exactly. He's using the wrong words to describe his point, which is that he doesn't think this particular mathematical language is useful. To someone who is fluent in that language, he makes it clear that he doesn't know how to use the language effectively (to stretch it, at times it doesn't seem like he even understands the semantics). But indeed, how could any sort of language be useful unless you know how to use it effectively?