Transformer short circuit test
In an open circuit test you can be sure that about 90% of the current taken is to magnetize the transformer's core. That current taken is due to the inductance of the primary (as if it were an inductor with no secondary). There are some resistive effects due to eddy current losses in the laminates and hysterisis loss too but these are relatively small compared to the dominant current of the magnetization inductance.

This means the dominant component is an inductor and this makes the power factor quite small.

In a short circuit test, it is the leakage components in the windings that are measured and, these can be quite similar in impedance i.e. dc resistance of secondary is of the same order as leakage reactance of secondary and ditto for the primary. This roughly (and with some hand-waving) makes the power factor round about 0.5 but could be as low as 0.2 and as high as 0.9.

The open circuit test will show a power factor that is likely to be below 0.5 and probably in the realms of 0.3 or less.

I am generalizing here and clearly some transformers (especially those used in flyback converters) have very low magnetization inductance but, for the average 50Hz/60Hz power transformer, the above will be the case.