That depends on how the seeds are generated. But I am sure it would be random and not selected from a list. And the probability of having the same seeds randomly is almost 0.
Almost 0 doesnt mean that it is imposible because there is still a posibillity for that. He might have been lucky enough to notice it and exploit it further. Although this all is a pure speculations and theories on how he did it, it hasnt been proven yet that two account rolling with the same seed could generate the same server seed.