Except in reality his targets weren't entirely dead, there were still millions left so he still went about killing the rest[0..2].
The intent in this case existed alongside unintended causes, but it was still there.
[0]https://en.wikipedia.org/wiki/Spanish_conquest_of_the_Aztec_...
[1]https://en.wikipedia.org/wiki/Spanish_conquest_of_the_Inca_E...
Imagine a hit man showing up to work one day, only to find his targets already dead along with their entire town... and only much later finds out that it's because he'd been an asymptomatic carrier for weird space germs when he was casing the joint the previous month.