Otherwise, your 12-word seed phrase is as safe as 24-word seed phrase if attacker doesn't know your seeds. But if one knows seeds but not their ordering, then 12-word seed wallet will be vulnerable to attacks but 24-word seed phrase still maintains high security.
Why somebody would know your seed at first place? (Regardless of whether its in or out of order). The security of your seed is must, even if you have 24-word or more seed. I have written seed of my wallet on paper and is never stored digitally.
If you read the article, its written that guy won a prize of 30$ for breaking this 12-word seed. From this prize money one can see the difficulty level of this task.