Can you merge two facebooks?

If someone has two facebook accounts, and he/she hided her friend list on his/her other facebook. When you click "find friends" and typed her name on mutual friend, exact same friend list shows up there. None of her friends on her original facebook has her other facebook as her friend. How is this possible without adding everyone again? Does this mean this person linked two accounts together? How does it work? Does this person transfered his/her friend list? How do you transfer your friend list on one facebook to another?