We don't know who the Rusiyyah of Ibn Fadlan actually were. They may have been Rus', but it's commonly assumed they were vikings, likely from eastern Sweden or Gotland. "Orgy" would be a very euphemistic description of what he actually describes, which is the rape, gang-rape and in one case a ritual gang-rape and murder, of women held in sexual slavery.

Whether or not Ibn Fadlan's account is correct or refers to Swedes or Rus' it's a well-attested fact that Swedes and other Scandinavians in the Viking Age had slaves, and female slaves were commonly used as sexual slaves and raped. This is not specific to the Viking Age or pagans, as the instutiton of slavery in Scandinavia survived several centuries into the Middle Ages after the end of the Viking Age.