Washington Irving, the writer of this American tale introduced many Americans to aspects of the European Culture.
Maybe his interest in Europe has started when his brothers sent him abroad for a 2 year tour of Europe (after he showed signs of tuberculosis),where in his notebooks he steadily became an acute observer and felicitous recorder of what he witnessed. Later on in his life he has also spent a lot of years in Europe where he met Sir Walter Scot who helpfully directed Irvings attention to the wealth of unused literary material in German Folktales. This is where Irving found the source for 'Rip van Winkle'.
Before the real story begins, Irving introduces Diedrich Knickebocker; an old gentleman of New York, who was very curious in the Dutch history of the province, and the manners of the descendants from it's primitive settlers.
Diedrich Knickebocker was one of Irvings pseudonyms, and so I believe that Irving himself, just as the by him created Diedrick Knickebocker, was very curious in the Dutch history of the province and the manners of the descendants from it's primitive settlers.
'The mountain episode' contains a lot of Dutch aspects, which show Irving has done some research like he said himself about Diecrich Knickebocker.
For example the fellows Rip van Winkle meets at the mountain are Hendrick Hudson with his crew of the Half Moon according to Peter Vanderdonk. ( "He assured the company that it was a fact, handed down from his ancestor the historian, that the Kaatshill mountains had always been haunted by strange beings. That it was affirmed that the great Hendrick Hudson, the first discoverer o the river and country, kept a kind of vigil there every twenty years, with his crew of the Half-moon, being permitted in this way...