Yes, that very well may be. The note was based on McPheeters' comment on p. 40 of the text.

George Martin

Battle of Helena

July 6, 1863 - About 12 M. they [Federals] place a battery on a point about 2 miles east of the hospital and commenced
firing shot and shell, but our men had gone some hours before. Some 6 or 8 struck immediately about the building, one
in fact went through the cabin where some or our wounded were. This created so much alarm that I ordered a large white
flag to be raised fearing that we might be injured by the shell falling thick around us. In a short time the firing ceased
and soon thereafter Col. [Powell] Clayton of the Kansas 5th Federal rode up with a squad of cavalry and asked why the
white flag was raised. I told him that this was a hospital, and as he had not respected our yellow flag I had ordered the
white one to be raised to [prevent] our wounded being injured. He stated that he had not observed our yellow flag.

Note: Clayton was elected governor of Arkansas in 1868