The Dread Pirate Roberts is a fictional character from The Princess Bride (book and movie), who in the novel turns out to be not one person, but a title given from one retiring pirate to the next successor because it's easier to work as a pirate when everybody is scared of you.
In this case, it's a fun way to hint that Silk Road is not operated by a single person, but by a group from what I think are US-Americans. There I merely speculate: I think the movie was a success in the US but not much in any other country. In fact, the only people who've quoted the movie to me are US-Americans.
Can people from other countries weigh in on this? Would non-Americans choose this as a pseudonym?