I can claim any level I want, for any language. It doesn't mean I actually am at that level.
Should I list French as one of my languages because I know a few words? To me, I'm not actively using it, and I am concentrating on other languages, so I choose not to list it.
I don't even know what my true level in German is. I know my writing is better than my speaking, so should I go with that level? or should I be more conservative and choose the speaking level?
If I choose to be conservative, and pick A2 for my level, then I am more likely to understand someone who replies back to me in German if they communicate based on the level I indicate.
I could go and choose to mark myself as C2 in Chinese. However, if you started a conversation with me in Chinese you would see my claim to be false. Then, you would have the right to question my other levels.
I have seen people who mark a high level in a language, yet communicate poorly in the language. I've also seen the reverse (as with Miriam).
I wouldn't expect someone who is a C2 level to be asking basic questions about a language. Now, I'm excluding vocabulary from this, because vocabulary is dependent on where you live and what you do during the day. Specialized workplaces require specialized vocabulary at times. While words may overlap at times, definitions can vary from field to field. A computer "core" is different than a "core" set of classes you must take in school.
I choose to be realistic with my language levels. I didn't even change my German level until more recently. And even then, I went with the more conservative level I was told.
So, perhaps C2 is his goal for Chinese, and not his actual level.
And, given the choice between him and you, if I needed a Chinese question answered, I would pick you. And the Native vs. C2 wouldn't be the deciding factor.
I'd choose you because of the attitude behind the answer. While he wants people to know the answer, it seems you want people to understand the answer.