Is Chinook then the language-group of the Kwakiutl?

The Chinook Jargon is a pidgin-creole (link). As a result, it has heavy influences from more than one language family: Wakashan (link), Chinookan (link), and Indo-European (i.e., English). The word potlatch probably has its origin in the Nuu-chah-nulth (aka Nootka) p'achitl. (Many Native languages of the Pacific Northwest have complicated phonologies with ejective and glottalized consonants.

The term Kwakiutl (an innovation of Franz Boas) has mainly been replaced since the '80s by the ethnonym Kwakwaka'wakw. Their language, Kwak'wala (link) is in the Northern Wakashan language family.

Ceci n'est pas un seing.