The same campaign traits on pages 54-55 of "The Worldwound Incursion" are completely different on pages 5-7 in the Wrath of the Righteous Player's Guide.
Huh?! Paizo folks? Bueller? Bueller?
can enhance his existing campaign trait (see page 8) if he
chooses a path associated with that trait.
The PC gets whatever it says in the Player's Guide, plus if the mythic path matches the campaign trait's associated path, they also get the stuff listed in the adventure on pp.54-55.
The additional story element doesn't happen until the 3rd volume of the adventure path, so they don't learn that stuff until then. But I believe from the phrasing quoted above that the additional benefits commence immediately upon gaining Mythic status - if the trait matches.
(And I'm not sure it hurts anything if the GM allows the added benefit even if the traits mismatch - but that would be a houserule only needed in order to encourage diversification of traits.)
They also act a bit like story feats. In the third book they're supposed to have optional plot tie ins.