It could. Take a look at that county by county map floating around. Many of those dark blue spots floating in a sea of red dont correlate to any city of significance but do correlate to reservations.
The whys of why that would be true I dont know. I do know that the tribes here and the Dems have been in bed together for a long time. Big kickbacks and special arrangements. Of course, the average indian walking around doesnt necessarily know about those things as most dont pay attention to politics any more than the average American. Maybe theyve bought into race politics that the liberals specialize in. One of the tribes near me has long abandoned their "culture" except when convenient and as a group has been pretending to be inner city blacks for a couple of generations now. Bernbots are often big ecowhackos, many of those in the tribes have bought into the false mysticism of the whole aboriginal living in harmony with nature thing. It could be that if you were to ask them they would tell stories of the social programs they relied on to provide food when they were kids. The wealth redistribution situation buys a lot of loyalty in children. Probably a combination of things.
This is some of my suspicion. Neither was raised on the reservation but there is contact there. That's the only factor I can come to as to why they have such a differing conclusion to the same evidence we have.