Being very familiar with Oklahoma pottery sherds I would say it is. It's been exposed to a lot of water erosion, and probably has washed down far from where it was originally left, so there may not be any others in the immediate area. Remember that Oklahoma was under the sea once and it is similar to some sedimentary deposits I've seen there. We hardly ever kept pottery sherds in Oklahoma. We did learn to hang onto the rim sherds, because you can ID the culture from them. We were out one day and a friend of mine found a piece with a full fingerprint preserved in the clay. I thought that was too cool.