That's the current revisionist spin, at least. Biological warfare has been practiced in Europe since the era of the Black Plague, if not longer. Catapulting infectious corpses over city walls was a proven method of weakening a besieged community. The spanish didn't even need to use blankets in the Caribbean. Completely disregarding their toxic belief system & their inherent parasitic nature, their septic presence on its own was lethal to the Indigenous populations of the region.