Those players are in the company of friends from the target realm

When traversing Azeroth, players may encounter players from other realms who share their same realm type. PvE with PvE, PvP with PvP, RP-PvP with RP-PvP, and RP-PvE with RP-PvE.

The exception to this is that wow gold players are freely able to invite Real ID and BattleTag friends to join their party, even if their realm types do not match. In this case, players will be randomly placed within a party member’s realm. While it might be a little disconcerting to know that players from non-RP realms are adventuring in RP realms, or that players from PvP realms are exploring PvE realms, this is working as intended. Those players are in the company of friends from the target realm.

Please keep in mind that if you choose to group with Real ID and BattleTag friends, you may be placed on a different realm type depending on the members of your party. As such, we recommend grouping with players who belong to realm types you are comfortable with experiencing (such as PvE or RP).