I am assuming that they were Hart's Dallas Artillery. They may not have been. General Hindman sent a detail from Pine Bluff to Fort Washita to retrieve 6 Parrot guns, which were sitting idle there because Pike didn't have the harress and other gear to use them. This was about the time that Gen Sam'l Curtis reported 25 pieces of artillery crossing the Mississippi river into Arkansas. So Hindman had the harness and equipment but needed better weapons. Naturally Pike didn't want to give them up and that was part of the problems between him and Hindman in the summer of '62.
Since Hart's Battery was being reorganized at Pine Bluff at that time and Parrot guns are shown on the Fort Hindman diagram at at Arkansas Post, I would say this is how they got there.