No wonderの後ろにthat節（文章のような句）を置くこともできますし、no wonder単体でも使われます。
A: Many Japanese people can't speak English, but your English is good.
B: Actually, I lived in Hawaii for a couple of years when I was a child. And I learned to speak it at that time.
A: Oh, I see. No wonder. (= No wonder you speak English then.)