The margin between them being about twice Clinton’s advantage. This is not an anomaly, as it follows similar results in other polls. The writer of the linked article makes his arguments as to why, but it really comes down to Clinton’s negative ratings with independent voters. Most independent voters aren’t socialists, but they don’t hold it against him. They see him as principled.
They also see Clinton as corrupt and Trump (whose unfavorability ratings are over 50 percent consistently despite the stubborn angry white crowd supporting him in the primary) as nuts. It’s that simple.
It does strip away the unelectibility argument Clinton keeps offering about her primary opponent. Bernie beats all of the Republicans in the polls, and by a larger margin than Clinton – although in this particular poll he actually loses to Cruz and Rubio while Clinton beats them, all within the margin of error.