Not exactly new to have tribal fights in PNG, probably over something trivial like a stolen pig. Tourists have previously been robbed on the Kokoda trail as well, and anyone walking around Port Moresby at night is guaranteed to be mugged, during the day it’s extremely likely.
I remember hearing that PNG receives the same number of tourists in a year as Australia receives in half a day.
With it’s natural attractions and proximity to SE Asia, PNG could rival Bali or Fiji as a holiday destination if the chances of falling victim to violent crime weren’t so high.