Aritcle doesn't appear to have any explanation of why the Democrats fielding a candidate is in any way dependent on what the Republicans are doing. Over in this article it says there are 5 Democratic (and two other Repulicans and two Libertarians).
Are they saying the Montana Democratic party decided to just phone it in with a bunch of nobodies because the incumbent appeared to be running for re-election? And they would have tried to actually find a good candidate had he withdrawn earlier? If so, that's on those people for choosing not to fight for it in the first place.