Good points, but it might not have been solo combat, two groups might have met, one opponent shot him with an arrow, another bashed in his head. They were too busy with his comrades to worry about looting his corpse at the time (and may not have survived the encounter.)
The arrow could have been broken off and lost in any number of ways.
"We analysed samples, scrapings from the knife, the axe and from his jacket and it indicates that the blood samples are actually from several different individuals," Dr Ian Findlay, of the Australian Genome Research Facility in Brisbane, said."