Below is the short history of the unit from Arthur Bergeron's "Guide to Louisiana Confederate Military Units, 1861 - 1865" (LSU Press, 1989)
There could be many reasons he joined in Louisiana. One Alabama native joined a north Louisiana unit while in Shreveport on business. A north Louisiana native joined an Arkansas unit because Arkansas was closer to where he lived than Shreveport was. Maybe the bounty for joining a Louisiana unit was higher or the Texas cavalry regiments recruiting near him may have been dismounted, thus losing their appeal. He could have been conscripted into service or hired as a substitute to take another man's place in the service. Too many possibilities to speculate.

6th Regiment, LA Cav
Col- William Harrison
Lt. Col- William B. Denson
Majors- __ Delacy; William J. Scott

Co. F- Capt. A. M. Alford

"The exact date and place of organization of this regiment remain a mystery. Several companies were added to Lt. Colonel William Harrison's Cavalry Battalion, ossibly as late as January, 1865, to make a regiment. Some records indicate the regiment existed as early as September, 1864. Whatever the case may be, the regiment saw little, if any, fighting during the war. Most of its service consisted of courier and guard duty around Shreveport and Alexandria. Individual companies of the regiment may have conducted independant campaigns against deserters, draft dodgers, and Jayhawkers in northern and western Louisiana. At various times, Harrison's regiment composed part of the cavalry brigades commanded by Colonel William G. Vincent and Colonel Isaac F. Harrison. Toward the end of the war, the regiment was dismounted and attached to an infantry brigade. The regiment appears to have disbanded with other units near Mansfield in May, 1865."