You know they prefer non-binary pronouns and still referred to them with "he" and "his". Maybe you're a non-native English speaker, and struggle with gender and grammar. Or maybe they have a point.
You’re rudely assuming an awful lot: 1) that it was me who referred to the person with an unwanted pronoun, as opposed to simply witnessing the person get upset by a third party doing so, and 2) that someone who insists on the identity of a non-binary male necessarily does not want to be referred to with the pronoun “he”. Pronoun preferences are just as diverse or contrary to others’ expectations as the labels that people apply to themselves.
EDIT: I was wrong. See below.