"Another band of Absentee Shawnee, with a band of Delaware, located among the remnant Caddoan tribes on the Brazos reserve in Texas, were removed in 1859 under supervision of the United States Indian agents, to the Washita River, where they came under the supervision of the new Wichita Agency."
-- end of quote --
So they had just arrived in Western Oklahoma 2 years before these Shawnee signed that treaty with the Confederacy was signed.
Then she says--
"The Absentee Shawnee living in the Wichita-Caddo Reservation were represented by their chief John Linney, among the 11 tribes that made a treaty of alliance in August 1861, with the Confederacy at the Wichita Agency. Some of the Absentee Shawnee served in the Confederate Army. Most of the Absentee bands, however, left the indian Territory for the Valley of the Walnut River, Kansas, where they remained as refugees during the war."
-- end of quote --
She then goes on to say by a treaty (never ratified) in 1867 they agreed to settle just to the west of the Seminole. They moved there in 1868. It says the land was later found to have already been assigned to the Potawatomi. The rights to their lands were finally granted in 1872. She speaks of a couple of bands of other Shawnee in Kansas who came back to the region aroung Shawnee-Tecumseh-Little Axe (just east of Norman) where the Absentee Shawnee still live today. So the band with the Caddo are just a small part of the Absentee Shawnee. She says the people of kansas demanded they leave, siilar to what Texans had done a couple of decades earlier.
Vance