The Kyza were the first group of people to settle on Sehto - and never numerous in population.
They ended up taking a strong linguistic deviation from the culture they'd budded from (quasi-African), something most obvious in their mythology and belief system. They lived on Sehto from 300 to the whereabouts of 800, when they came to have their land contested by Xhosa settlers that had followed their routes to discover Sehto a second time, and were regrettably quickly killed.
Not much of Kyza culture remains accessible today, though the names of their settlements have endured (albeit not without alteration) to this day. Whether they truly settled on Sehto or had a more mythological relation to the Xhosa is in dispute, less for lack of Kyza settlement clues (it's clear someone lived on the island when they allegedly did) and more out of question of cultural identity. There are theories the Xhosa simply came to the island earlier than their own records show and then split into two groups while on the island, rather than arriving as a second wave of settlers.
The Xhosa speak of the Kyza in largely mythological contexts, further obscuring the line between historic fact and fiction.