I learned it from my grandmother and from Gladys's grandkid. Gladys was the last person whose first language was Kiksht, not the last person who speaks it.
Maybe there are some sources talking about fully fluent people still being alive? As currently the article gives the impression they were the last person to "fully" speak it.
I’m aware and I think people do not care much to correct it. The tribe has had consistently bad experiences with outsiders attempting to document this kind of thing and I sense that people are mostly wanting to be left alone at this point. There is some possibility that I would make a different decision, but it’s not for me to decide, it’s for the elders.
https://en.wikipedia.org/wiki/Upper_Chinook_language