Hmm. Could a Wavedancer live so far from the sea?
I don't know what tribe Teir's father came from-- but the book "Kahvi" makes it clear that magic gifts could spring up suddenly and spontaneously among the Go-Backs. There was a little guy who could lift small objects-- and upon questioning, swore he was no descendant of Rayek's.
The gift apparently shared by Teir and his father seems extremely rare, perhaps even unique. I could easily believe Teir's father was a Go-Back too. Or, possibly, there is still another unknown tribe or two out there.