First of all, the HERV-K virus is present in the human genome, in fact it is one of the most common endogenous retroviruses there (see references 1 and 2).
In a viral infection, these proviruses get integrated into the human genome and can be found later there. This is a useful tool when you want to find out details about the split of closely related species like the great apes and humans. If you find such a provirus in all analyzed species, the integration must have happened latest at the last common ancestor. If it is only found in a part of them, it happened after the species divided. The figure (from reference 3) shows this shematically:
The authors of "your" article did this and found the integration of the retrovirus in a specific locus in the genome of gorilla, chimpanzee and human and found it only in the first two. From this they conclude that the apes are closer related to each other than to the human.
So in summary it means that the HERV-K is not present at one specific site of the human genome, not in general.
- HERV-K: the biologically most active human endogenous retrovirus
- HERV-K(HML-2), the Best Preserved Family of HERVs: Endogenization,
Expression, and Implications in Health and Disease
- Differences in HERV-K LTR insertions in orthologous loci of humans
and great apes.