I didn't know where Dutch comes from either, so .... yay for searching online ...
"The word Dutch comes from a Proto-Germanic word meaning “of the people.” It shares a root with the German word Deutsch, which has led to some confusing names. The name Germans call Germany, for example, is Deutschland and the people there Deutsch. Dutch and German are related, after all, both being Germanic languages."
Given our history with the Germans, it seems a little ironic. But this supposedly stems from the 1500's, and stuck globally.