The pension application has only one place to list a veteran's military unit, so even when a soldier served in several commands, it's not unusual to find just one unit listed on his pension application.
Many officers and men of Voorhies' 48th Tennessee Regiment and other infantry commands recruited in Tennessee left to join cavalry commands raised in their home counties. Biffle's 19th Tennessee Cavalry carried the names of many former infantrymen on its rolls.
Also, a cursive "I" often looks exactly like a "J", so J. H. Coffee listed as Biffle's adjutant could well be I. H. Coffee, formerly of the 48th Tennessee Regiment.
I would need to check the service files to get a better idea about this.