Magical people

From TLJwiki

A phrase usually used to refer to the five races of Arcadia who were entrusted with pieces of the Stone Disk; namely, the Venar, the Banda, the Dark People, the Maerum and the Alatien.

Although there are many other races in Arcadia - such as the Dolmari, the Stickmen, the Orlowol or the Sunriders - the folk entrusted with the Disk seem to have particular gifts, like the arcane magic of the Dark People or the 'earth-singing' abilities of the Banda. This might be why the fragments were entrusted to them in particular, as they are better placed to protect them than the others.