the issue in kashmir is, in fact, quite clearly internal, and up to the local actors to work out. that is not debatable.
everything else aside, i don't think it's very intelligent for sanders to come out and take a side on an issue like this, which has been going on for decades and requires careful diplomacy, if the united states is to involve itself at all. if the intent is to go for specific demographics, i'll remind you that the number of non-muslim indians in the united states is not exactly trivial, and that this isn't an issue where their "side" can be discounted or ignored. the indian government does, after all, control the region.
i want to hope that what bernie was trying to get across is that he recognizes that lingering instability in the region is not in the interests of the united states, due to concerns about migration (in the event of a serious conflict) and the deadly possibility of nuclear war. unfortunately, what he actually got across was that he's taking a specific side, which is neither likely to help his own poll numbers (he's increasingly coming off as a tool of muslim blood money) nor make him look very good, internationally. further, if he was going to take a side, he's on the wrong side of the greater geopolitical situation, as pakistan is more or less allied with the chinese at this point. the better tactical decision would be to come in on the side of the indians with the intent of containing the chinese; when you come in on the side of pakistan, here, you're just playing into the long term strategy by beijing.
the indians have long memories, and they don't take too kindly to this kind of thing. so, what he's accomplished by running his mouth off when he shouldn't have is having the most important power in the conflict interpret him as an unfair mediator, which is just going to further harm the people that he's nominally trying to protect. i would be equivalent to calling for an international presence in the west bank - something that's just going to get you seen as an adversary in tel aviv.
so, right or wrong - and this conflict is messy. there's no clear outcome. and, nationalist uprisings are passe. - what he did was pretty dumb, all around. it will probably cost him more votes than it gains him, and it restricts the ability of the united states to actually mediate, if he happens to win in the end.
he should have said something along the lines of that he regrets the loss of life and looks forward to working with both sides of the conflict to end the violence.