I don't see why the state is giving in to the tribe.
I am not an attorney, so I probably am not qualified to interpet it all so take this for what its worth, but here is my opinion. In the court case "Skokomish Indian Tribe, Appellant, v. E. L. France, Trustee, et al.", it appears that the court is stating that the reservation only included uplands. They were dealing with tidelands, but give several reasons why they believed the tide lands were not included. Most, if not all of these would appear to apply to the river too. The treaty itself only lists the reservation bounardary as to the mouth of the river and up the river. While this may be vague, it is clear that the reseveration was split up and divided among tribal members. I do not believe any of these allotments includes the river or land under the river. (I could be wrong but the previous court ruling indicated that the allotments were all up lands). In addition the ruling case also states that it is clear that the reservation was meant as an area to reside and not as a boundary for economic means (fishing, claming, hunting , etc), it also mentions the common practice of high water mark being the boundaries. There are other reasons but you can find them yourselves if you read the ruling.

Another interesting case mentions that among the tribes at that time, they commonly recognized the half way mark of a water way as a boundary among themselves. Meaning, at worst, that if they thought they owned the river, they would have most likely interpreted the boundary it as half.