Power factor of a transformer (does it have anything to do with load impedance)
The power factor measured at the input side of a transformer is mostly determined by the load. Unless the load is very small, the effect of the impedance of the transformer itself is almost negligible.

The power factor measured at the primary of the transformer is the result of applying the source voltage to the combined impedance of the transformer equivalent circuit and the load.

The power factor at the secondary of the transformer is determined only by the load circuit. If the load changes, the power factor changes according to the change in the components of the load circuit that are responsible for the change in load.