Okay I just figured it out...on the Heritage Quest website where you can look at actual census pages, they have a portion of Yell County mislabeled as Woodruff Co. I wonder how many folks have looked for their relatives in Yell county not knowing they are mistakenly listed under Woodruff Co, Magazine Tsp. So there they are. I guess I may notify Heritage Quest of their error.

This is probably the correct family of the soldier. A lot of 4th Ark Cav folks come from the river valley area, but many had to travel north to enlist where the US forces were stationed more permanently.
However, as to his death date I question the accident in an auto before 1900 as there probably were none in that neck of the woods. On his CSR it states that someone requested another certificate of service since he lost his discharge. Then on Dec 13 1890 it states he is dead and it lists the widow's application number, so this particular William Davis did not live past 1890 and definately probably not die due to an automobile accident as stated on the Findagrave site.

My opinion is William Davis of Co M 4th Cav is probably Wm Davis of Yell County. Perhaps some family stories got a little mixed over time and as they were told down through the generations.