I think it means that the borders of Oklahoma get more complex when you consider the treaties that the US has entered into.

It's worth noting that according to the constitution, treaties have equal weight to the constitution. Therefore this ruling seems to me a way of saying "hey, maybe we should draw the maps according to the highest law in the land".

It has a bonus effect of signalling that the native people are actually people for both punishment AND benefit. Traditionally the US is bad at acknowledging the benefit side for folks with pigment (and doubling down on the punishment side, but that's a different discussion).