'.......I did not introduce anything into my tank that had bba spores......'
Incorrectamundo!!!!! The spores didn't materialize from nowhere.
This is not a difficult process, since you have no live plants, but it may take time and diligence.
Bleach dip all decor and use plenty of water conditioner on all bleached items before returning them to the tank.
Then as you see BBA on sections/pieces of gravel, suck them up with a siphon tube being as thorough as possible, and either bleach dip them or boil them, and then replace them into the tank. Initially, you might want to collect sections you see the algae on and when you have a quantity of it bring it to a boil and let it cook for a few minutes.
This will kill anything in/on it. OR, you can spread it on a cookie sheet and pop that puppy into the oven at 350° for 15 minutes.
BBA is persistent, but if you keep after it, it will decline.
Len