@jlou “Consent is primitive” in this context means that the notion of a right is defined in terms of consent. For example, “one has a right to X if one's absence of consent for not-X compels others not to deprive one of X” is a definition of rights in terms of consent.
(It is an objectionable definition, but i'm just giving an example)
One could then define consent in terms of further primitive notions, or take consent itself as a primitive.