Tahrif in this historical account means alteration of an inherited Abrahamic tradition by later unauthorized religious innovations. Idolatrous practices developed among the descendants of Ishmael despite the earlier heritage.
The account associates the spread of such practices with ‘Amr ibn Luhayy and mentions invented restrictions involving animals, divination and other customary rites.
The underlying principle is that attribution to ancestors is not sufficient to make a rite religiously authoritative—especially when the rite contradicts the governing principle of the tradition it claims to inherit.