It appears that it was Lt. Col. E. J. Searle's 1st Ark. Inf. (US), as they show up in the order of battle listed for Jenkins' Ferry in Edwin C. Bearss' "Steele's Retreat From Camden and the Battle of Jenkin's Ferry", while the 1st Ark.(AD)(46th USCT) does not.
Set in the context of being a Unionist paper trying to gather even a glimmer of a positive out of debacle and the statement of the fact that "Pete" was attached to headquarters and not mentioned as being on the line with a gun, I propose that he was one of the "colored Americans gathered to us since we started" that are noted in the aforementioned history of the event.
I hope this clears up the confusion a bit.
Richard