Doyle, I believe that part of Sergeant Meiars' narrative is the result of a hazy recollection of events. Shortly after their arrival in Virginia, according to the battalion muster rolls, several members of Captain Lacy's company were detailed to serve temporarily in Cook's Virginia Battery. I believe this is the artillery experience that Sergeant Miears remembered.
It's always been my understanding that the three companies were recruited as infantry, with the intention of attaching to the 1st Arkansas Infantry. However, the War Department refused to permit the 1st Arkansas to exceed its authorized strength of ten companies, so the men were assigned to various detached duties until it was decided to organize them into a separate battalion. In addition to the details to Cook's Virginia Battery, several men (mostly from Captain Beavers' company) were detailed as "marines" aboard the CSS Richmond, and others were detailed as provost guards at Camp Lee, near Richmond.
It looks to me that the War Department was caught by surprise by the sudden appearance of an additional three full infantry companies, and weren't sure what to do with them, so they assigned them to "busy work" until someone decided to form them into a battalion. And what a battalion they became!