It's unjustified to call it "bioterrorism" if it wasn't intentional. The first documented cases of biological weapons actually predate 1492. I don't remember when they were first used but it was well before 1492. It involved putting blankets used by sick people and throwing them at the enemy with catapults. Other methods involved throwing decaying corpses with catapults.
I don't think the smallpox helped Cortes. His conquest was so quick it couldn't have had an effect. Do you have any evidence it had an effect? I haven't read anywhere that it helped Cortes.