When Rowan became a Legendary as an Ouroboros Serpent, his Bloodline Talent was corrupted by Chaos, and due to the fact that he was very weak at that time, he was helpless against this manipulation of his destiny.
The only way that Chaos Blood was added to his bloodline was during the period that his bloodline had been linked to his Bloodline Source.
Now the wheels had turned and he had access to a place like this, he knew how powerful the abilities that were stored there could be, and it once more proved the depths of the Demon King's influence over the Lightning Kirin bloodline.
Perhaps, he still had further designs for this place, and Ohrox intended to invade their Bloodline Source in the future.