Anyway there is no reason for it to keep happening. Just have a "main character" flag on your MC that makes NPC initiate dialogue only with him. They only have this kind of mechanic when talking to companions (you can't make a companion talk with another companions, the game will change to your MC when you try it)
Even in a multiplayer game they could create a clear distinction between "Player character" and "NPC follower" and avoid this issue regardless.
IF they cared enough to bother, I mean.
