Hey there, forest pest management is my job. Finally I have something to contribute to this forum (as it sure isn't barbeque tips yet, although I'm quickly getting the hang of my UDS and have figured out what a fatty is).
Both termites and carpenter ants need a moisture source, so whatever you picked up was probably in the wood before you brought it into the garage. Look at the tunnels in the split wood. The tunnels of carpenter ants are very smooth and clean; termites have bits of mud and mess inside. Given your location (Dearborn), I'd guess carpenter ants.
Each carpenter ant colony has one queen. Chances are as you cut the tree or repiled the wood, you didn't bring her home. So you likely have workers slowly dieing off with no replacements. They have probably been confined to just a few pieces of wood, although may scavenge for food especially at night. Carpenter ants do not eat wood. They only hollow it out for their nest (if there is a moisture source).
I would just keep an eye on it. Check around the pile after dark. If you don't see scouts all over, your roof isn't leaking, no puddles running from your car into the woodpile, etc., you probably have nothing to worry about. That said, don't leave it around indefinitely; yes, now you have an excuse to fire up the smoker every weekend.
Hope this helps.