I dont understand, what is the relevance of playing expertise when it comes to website design.

It isn't very relevant. But all Jeremy knows about you is what you write. That is somewhat relevant to website design, since in coding and running a website you have to both get the details right and think about how you come across to your readers. You come across as someone who can't edit his way out of a wet paper bag and doesn't care how difficult his writing is to make sense of. So why should Jeremy pay any attention to your suggestions?

Nick was pointing out that it would have given you a bit more credibility if you demonstrated that you were good at something, even if writing wasn't it.