Intuition wouldn't be able to accurately assess whether one was a Dark Child. One needed to sacrifice part of his vitality from his very core to reach for and nudge at the other's true essence. If that didn't trigger a response, one would then be able to conclude firmly that the other wasn't a Dark Child!
The black-robed man hadn't intended to make use of his own life essence as he hadn't thought that Wang Baole was a Dark Child. The Dark Sect had fallen a long, long time ago, becoming a mere legend. There remained few signs in this world that still proved it had existed before.
The sudden appearance of someone who might be a Dark Child invited incredulity from the black-robed man. After allโฆ even during the height of the Dark Sect's glory, there had been few who had been able to become a Dark Child.