This duality is derived from two phrases. The first beeing the "The Stanger". Where one sits on his hand until all feeling is lost, then masturbates with said hand giving the feeling of a stanger doing the work.
The second part of this is derived from the "Dutch Rudder" where one grabs his erect penis and has another work his arm back and forth for the purposes of masturbation.
The Strange Dutchman is a combination of both, Where one sits one his hand until all feeling is lost, grabs his erect penis, and then has another work his arm back and forth for the purposes of insanely awsome masturbation.