If this is about the First World War, “casualties” and “fatalities” were reported separately by some nations. So “casualties” were soldiers who were injured but survived, whereas “fatalities” were those who did not.

Ergo, the Sikhs had fewer casualties but more fatalities, as soldiers without a helmet were more likely to perish rather than survive with injuries.

On the same note, there was a possibly apocryphal story about some British MPs trying to stop helmets being issued to to troops, due to them misunderstanding the casualty/fatality distinction and only seeing that “wearing a helmet= more likely to be injured,” rather than “wearing a helmet= more likely to be injured, instead of dying.”

(My apologies for the lack of sources, I’m in a rush at the moment)