The example does not exemplify the grammatical note, for the genitive here follows the preposition e)pi/ rather than the verb. As the verb in the sense 'abide by' seems always to govern a prepositional phrase (see LSJ s.v. I.6), the note is probably an error.
[1] Initially and tentatively ascribed by Adler to 'FGrHist 115', i.e. the historian Theopompus of Chios (C4 BC), theta 172, though in her consolidated addenda and corrigenda she changed this to '151', an anonymous Alexander-history. In any event surely pertaining to the most celebrated Olympias of that (or any) era, the formidable mother of Alexander the Great. See generally OCD4 s.v.