Its because they have linked accounts. Very simple, when you link accounts, you can play on one account twice. Now you can not
LOGIN twice on one account, you can play twice on one. For example, I have a linked account...I login on my unlimited one, then I login on my basic one, which is linked to my unlimited one. When you are linked, you get an arrow thing near your account name, before you click to play the game. Try lookin at my How to run POTCO twice on one CP, maybe it can help ye out
