Ernie Chambers is listed as an independent because the Demoncratic party is MUCH too right-wing for him.
The NE legislature is officially non-partisan, but it has been GOP majority for decades (at present 34R-14D-1C). Chambers isn’t a Democrat for the exact reason you cited. The only party he has supported was the “New Alliance Party”, which was Communist (whose label he ran under for U.S. Senate in 1988).