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.
Actually it still is pretty much impossible. Apart from seeds matching, we are also saying that someone happened to have seen the seeds and compared them. And I think Stunna did say it was a flaw he took advantage of.