Looks to me like a very sophisticated operation. They are working to shave votes/delegates from Bernie by enough to keep him from running away with it, but trying to keep it “credible.”
I am sure the goal is to keep Bernie below 50% in the delegate count at the convention to allow the superdelegates to come into play. And if you add up the poll percentages for all of the centrists, they significantly exceed Bernie’s percentage.
This means that if lower-polling (and delegate-count) centrists pledge their delegates at the convention to whichever centrist ends up in the lead, then that candidate will have more votes than Bernie, even if Bernie is leading all through the primary campaign. Add in the superdelegates, and it will look like the centrist is the legitimate winner at the convention.