Well drowning victims have water in their lungs and homicide victims probably don't since dead people don't breathe even if they were found face down in water.
Gunshot wounds or stabbing wounds might also be a pretty good indication of homicide.
Bodies with no wounds and no water in their lungs will be classified some other way, probably dehydration.
And since this guy's specific job was storing and cataloging them onto refrigerator trucks after examination, it's a pretty good bet they had toe tags with the pertinent information for him record.
The point is from my understanding of the article he was just helping load bodies. How would he know they had water in the lungs?