What is a Sheikah?
Then, are Sheikah Hylians?
The Sheikah are a humanoid race, bearing great resemblance to Hylians in both appearance and magical capacity. The Sheikah, however, are known for their distinctive red eyes and pointed ears, which they share the latter with the Hylians.
Similarly one may ask, what does the Sheikah symbol mean?
The Sheikah symbol is an eye with three triangles above it and a big tear. The meaning of this symbol is rather confusing, although it can be interpreted that the eye is a symbol of truth, a noun many times asociated to the shadow folk. The three triangles may symbolize the sacred Triforce, that they protect.
Although the Sheikah managed to seal Ganon away, they were banished from Hyrule for leading to the army of enemies terrorizing the land. The army seems to still be present in Hyrule in Breath of the Wild, manifested as the deadly Guardians seen in trailers.