To add to what has been said, the article notes that the Europeans responded well to infectious diseases- they quarantined and evacuated. This limited the spread and the overall lethality of any diseases on the Europeans.
But also the filthiness of Europeans protected them. Their filthiness had been developed over millenia as the population became more dense, giving lots of time for the population to evolve immunities (and for the diseases to become more potent).
This arms race meant that the diseases were tough, the Euros were tough, but those races who had been spared the arms-race of filthiness were sitting ducks to the Euro super diseases.
