Obviously you use an adjectival ending to indicate that it's an adjective, but it's still a form of "cineál".
I don't know how English ended up using "kind" to mean two such different things, it just seems like a calque that Irish uses the same word for the same two distinct things.
In English, it comes from the meaning around "kinship", where the adjective originally meant "with the feeling of relatives for each other".
In Irish, it may be linked to the meaning of being "true to kind" when referring to animal stock for instance. Also linked to the "natural" state of something, unaltered, again "true to kind".