لأن معناه كجزء معناها
Because its meaning is, as it were, part of her [kināyah's] meaning.
The comparison particle ka- (“as though”) matters. The meaning of kināyah is not a literal compound whose two mandatory components are the concomitant and the original assigned sense. Thus majāz cannot strictly be described as an actual constituent of kināyah's meaning.
The comparison instead contrasts a use restricted to the transferred sense with a use that also permits literal intention. Part and whole are an analogy here, not an assertion of literal composition.