Look at the higher resolution photograph of the stone, not at the graphic sketch, which is slightly misleading.
For the fallen man, you can see the back of his head, on which it is clear that the hair is shown, and not a helmet, as on the enemy.
Besides the head, at the edge of the stone, there is something that looks like a ponytail, in the same way as the hair of the victorious warrior is shown. Moreover, the ponytail of both warriors is tied with a chord, which has at its 2 loose ends some kind of knots or decorations. The 2 ends of the chord are seen for both the victorious man and for the fallen man, and they look the same.
The resolution of the photograph is not good enough to make the identification of the feature at the side of the head as a ponytail certain.
Nevertheless, the hair on the back of the head and the presumed ponytail look very much, at least at this resolution, like the hair of the victorious warrior, and very unlike the helmet of the enemy.
Because the enemy wears a helmet, we cannot know for sure whether his hair was short or long. We can presume that his hair was short, as otherwise the helmet might have been uncomfortable.
Also from the loincloth of the enemy we see just a narrow edge, which is not covered by the shield.
I agree that the lower edge of the loincloth is similar for the fallen man and for the enemy, and this is the only similarity between them.
So we have:
Pro the fallen man being an enemy:
Similar lower edges of the loincloth.
Contra the fallen man being an enemy:
1. Completely different military equipment, spear and helmet and shield versus sword with a scabbard of an unusual form (common to the fallen man and to the victorious man).
2. Long hair tied in a ponytail versus presumably short hair under the helmet
The similar lower edges of the loincloth might be explained by all loincloths being similar. The victorious warrior might have been a richer warrior and he might have had some more expensive leather garment instead of a loincloth, like most other warriors.
