Your hypothesis is in the right direction, though the powers don't seem to be very mystical, just unusual in his species.
Nero is of the species known as Anti-Birds which the wikia describes as:
Anti-birds are small birds that have black feathers on their back, wings, and around their face. Their faces have red feathers while their undersides have white feathers. Their beaks are black and they have a pair of feather that are shaped like downturned horns.
The Anti-birds are capable of sensing mana and will peck at those with low or no mana. Anti-birds will not approach anyone with high levels of mana and will become frightened when they get close to those with powerful mana
The wikia entry for Nero lists this mana sensory ability as what allows him to detect magical items and and help them navigate toward a source of mana. This utilization of the mana detection seems to be unique to him, as the wikia also mentions the following ways in which Nero differs from usual anti-birds:
Nero is the only Anti-bird that has upturned horns and two tail feathers shaped like arrows
Currently only Nero is shown to be able to detect magic stones and Anti Magic weapons
As you can see, there's no clear confirmation or reason why Nero is different than the others, but we do know that he is the only one who can do this.