In particular after it'd been sitting in the water in 90 degree weather for a few days.
I'd say it's racism but it would probably be hard to even tell the race.
Also I'm not sure how he know they drowned or how he knows for certain that some were homicides.
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.