It is not an incorrect use. I was explaining the previous clause (you are not a native English speaker).
"I am a native English speaker, whereas you are not, so I think I know my grammar rules better than you" retrouvailles
your so-called interruptive clause ("whereas you are not") does not explain the condition of the previous clause ("I am a native English speaker"). your "whereas-you-are-not" is a completely unrelated matter, and so it cannot be qualified as a legitimate interruptive clause.
read again my suggested version: "I am a native English speaker, whereas you are not. So I think I know my grammar rules better than you do"
now compare that with yours! the corrected version is far clearer.
a side note: being a native english speaker does not automatically mean that you know about grammar rules than all non english speakers. i lived in english speaking countries for ten years, and God knows how many the so-called native english speakers simply suck at spelling and grammar!
Also, you are still committing a great many errors in this thread, such as your lack of capitalization of the first letter of a new sentence and such things as this:
Why didn't you bother to correct that?
i never mind my spelling and grammar in a forum. in fact, i enjoy the informality and the fun they tend to generate. it was you who wanted correct spelling and grammar. if i wanted to make corrections of sumthing, which i did, it was merely becoz i wanted to have fun. is it hard to understand?