The only exception that might know Ainsley's secrets were the fairy of space or the fairy of soul and spirits.
The fairy of soul and spirits was the peak existence among those dwindling with soul and spirits.
He's like the founding father of shamans and all kinds of soul/spirit summoners, including otherworldly summoners!
It's not weird if he discovered Ainsley's secret once he saw her.
However, when Cellino said this, he didn't believe that Ainsley would be so 'lucky' to meet those kind of rare existences who could unravel her secrets.
It's simply too difficult to meet those existences. Among them, only the sacred guardians had a higher chance to meet Ainsley...but not all sacred guardians could see through Ainsley's soul.
Cellino could sense Ainsley's foreign soul simply because he mingled with Code-B from when they were an ordinary baby beast!