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.
Well every is a theory and impossible until it is proven so and we had no idea on how he did this so what we are doing right now are speculating on something that might come to sense.
The flaw could mean anything, more interesting is that on how he was able to find that there is such flaw that will reveal the seed on the site
I can 100% guarantee that is not possible. When seed is generated the same seed can not be generated on another account, its impossible. My best guess is he duplicated 2 same accounts and thats how he got a hold of same seed.
By what you meant as duplicated account , do you mean that he have 2 account with the same username? I dont think this is kinda possible because each sites got their own system restriction whenever someone is trying to register with the same username though