You might be stumbling about the fact that "Krapfen" is more ambiguous that your Krapfen = donut conclusion.
- The small piece of yeast-based dough, often filled and/or fried.
That's the category your "Krapfen" and donuts fall into. In many dialects they are also called "Kreppel". (And a bunch of other names.)
- Filled pasta dough, sweet or savoury, typically folded and/or crimped together.
While an Italian would talk about "ravioli", an Estern European about "pieroggi" and an Asian about "dumplings", someone from Southern Tyrol or the Allgäu would call them "Krapfen" (but also use the term for the variety above) and in Jiddish cuisine it's a "kreplach".
So if you want a donut, say so. The term krapfen won't mean anything to an English speaker (check your favourite dictionary, I just did!). But don't be surprised if you are offered kreplach and get a ravioli, not a donut.