Actually Greenland is mostly Innuit, or Innuit-European mix. Only 11 percent of the population is "European". Neighboring Iceland was settled by the same crazy bunch of Vikings back in 1000 AD , but it has a very low murder rate. The more ethnically uniform modern Icelanders are almost all descendants of these Vikings.
Eskimos have a high suicide rate in the USA, but not a large homocide rate. So its a mystery why the largely innuit Greenlanders would be unusually violent. But you have to take into account that the whole country has a tiny population size, so that each murder skews the rate.
Murder rates are done "per 100,000" of the population.
But the whole population of Greenland is only 56000. So if there were only one murder in the whole country that one would give it a "murder rate" of 2 (which is higher than "the rate" of most west european countries).
(Greenland is the same physical size as Mexico which has 100 million people, but only has only 56K people).
There were 11 murders the year it was 19.2. According to that same website Greenlands murder rate has varied over the last 15 years from a high of 30, to a low of 3.49. For actual murders that would mean something like 16 actual murders down to like 2 actual murders in a given years.
So part of it is probably a statistical fluke caused by the country's tiny population size. But still, they do seem to have more murders than they ought to for some additional unknown reason.