Exactly it would be like Mon Mothma refering to the Emperor as "Old Palpatine" or Leia refering to "wheezy Vader" while at the same time trying to convey how dangerous they were.
In ROTJ the Emperor is putting Luke down, making him sound weak and inexperienced by directly addressing him as "young" all the time (in the way old people in authority do).
In this conversation the Emperor is saying that Luke is a threat so it makes sense (if possible) to have him refer to Luke by his full name.