Cultural event
The dawn gnomes became their own people, splitting off from the group and developing their own magics and racial features distinct from other gnomes.
After having wandered and set themselves into seclusion, the dawn gnomes continued to adapt to their new environment and slowly change their form over time in tune with the magics of Plane of Faerie until finally becoming very distinct from the progenitor gnomes. They continued this life of seclusion, growing more and more distinct from other gnomes and became recognizable as a distinct race.