[dredmorbius]

It's possible that terms such as "Pennsylvania Dutch", which refers to the German-Paletine originating Amish and other groups within the US state of Pennsylvania, might account for some of this confusion. The "Dutch" in that case are actually "Deutsch", that is, of German origin.

That said, the Dutch language is among the Germanic languages, and is closely-related to German itself (similarly, the Dutch-derived Afrikaans, with which Dutch is largely mutually intelligible). To someone reasonably fluent in German, Dutch looks like a somewhat garbled variant. Similarly Danish, though the spoken form varies considerably from the orthography, and Norwegian, also closely related. Contemporary German shares many words and a fair bit of grammar with English as well, making blingualism in both relatively easy, compared with, say, more distant languages such as English-Arabic or English-Mandarin.