It can be assumed that the injunction was granted because of some question over the legal residency status of these students in the state of AR. Perhaps they are being told that as residents of other states, they are registered to vote there and required to vote there.
If they weren't legal residents of AR, then they can't be legally resistered there. If that's the case then perhaps the suit brought by the Dims has some merit. (As much as it pains me to say so.)
This argument should be brought in Wisconsin, where students vote over and over...