Parent specifically stated DNA viruses. From your article:
> Most of these viral genes come from retroviruses, RNA viruses that insert DNA copies of their own genes into our genomes when they infect cells. HHV-6 is unique because it is the only known human DNA herpesvirus that integrates into the human genome and can be routinely inherited.
https://newsroom.uw.edu/news/genes-%E2%80%98fossil%E2%80%99-...