I agree with your first two sentences. Mod parent up.
However, the right to a secret ballot is already in the Colorado constitution. (It's also in some federal legislation called HAVA.)
This is a federal judge, properly finding that plaintiffs haven't asserted any controlling authority showing there is a federal question in the case, so it's filed in the wrong court.
I have not read the complaint in this case. If I'd been writing the complaint, I would have used equal protection, tied into the state right to a secret ballot. Under Bush v Gore, if they do it one way in Denver, they should do it that way in Boulder too. But I don't think there was an equal protection claim raised.
(I'm a former election lawyer, and I'm a former Boulder County officeholder, and I'm aware of this case, but I haven't read any of the documents, so I'm speculating.)