If the New Hampshire primary had only included Democrats, Sanders would have only won by 4%.
But Reuters doesn't narrow it down to "independents who plan to vote in the Democratic primary" or even "Democratic-leaning independents." It's just "independents." Which includes tons of right wingers who have no intention of voting in a Democratic primary. Typical from incompetent Reuters. That's probably why Pollster only uses the numbers among Democrats.
Also, there are a lot of closed primaries/caucuses.