XD is he not a native English speaker? Don't think I've ever heard anyone phrase it as "coauthor at your storygame."
Love his bold capitalization choices: nothing but the second "t" of TacocaT, and the word "Good." Perhaps he's emphasizing just how Good he is at grammar grammer and spelling(s?)
I admire his confidence, if not his facility with the English language.
(Freely admitting here that any ESL site members are far better at English than I am at whatever language they speak. Just, y'know, 1) I'm not claiming to be good at other languages, and 2) ain't nobody better than me at English XD.)