Christian has shown himself to Jack in LA so he isn't limited to the island. He could have appeared on the freighter. I don't see how his words to Micheal could mean anything other than "time to die"... If the island were going to protect him wouldn't it just stop the bomb from going off?

As for Jin... He made it far enough to jump or be thrown from the ship. He could have caught some floating debris and arrived on the island before he left the ship ala the Doc Ray...