That poll was of registered Democratic voters for the Democratic candidate (and registered Republicans for the Republican candidate), and it's pretty consistent with nation-wide polling on the subject. Hillary Clinton leads by 30-50 points in just about every state, and then the native son or Joe Biden comes in second place with around 10-20%. For the Republicans, as the map and polls imply, it's a lot more divided and thus actually interesting.
The status of the Democratic Party in Montana is weird--although they cannot flip the state blue for the electoral college, they have two Democratic Senators and a Democratic Governor (who has a solid chance to become the next Democratic Senator in 2014 when Max Baucus retires). I think you were thinking of this
presidential geography blog post on Montana, which is still good reading. The short version: similar forces are at work here like in Nevada with West Coasters moving east into the conservative state, with college towns and native American reservations but fewer Hispanic groups.