I guess he was referring to those who weren't killed otherwise.
Which, in any case, in no way bears on the conclusion reached in the good doctor's letter to
Lancet, which is rife with historical inaccuracies, some of which I cite here
There were 3560 lifebelts aboard the ship, so presumably all those who died were wearing lifebelts...
...they were presumably floating with their heads above water...
Aspiration might have occurred after they became unconscious.
1. Since there is evidence in the debris field of bodies having reached the bottom, it is unlikely that all who died were wearing lifebelts.
2. The design of the belts did not guarantee that the wearer's head would be held out of the water. Since the flotation vector is symmetrical and low, I would expect equal numbers to float face-up and face-down.
3. Dr. Shetty's acknowledgement that they might have inspired water after losing consciousness undermines his major premise, since any who did would have drowned before succumbing to the cold. This would suggest the opposite of his hypothesis.
The other possibility, which I think can be supported statistically, is that most of the 1,200 missing victims went down inside the vessel. These unfortunates would have drowned long before the cries of the freezing ebbed.