Disturbances are internal and external factors. In PMSM load variation is a disturbance and this can be easily provided through the load torque. Supply voltage fluctuation is also external and can affect the behavior of the PMSM. In terms of the internal disturbances, we are talking about parameter variation, harmonics, temperature effect. These internal factors are not included in the block you are pointing at. However, Simscape Electrical provides also a FEM-Parameterized PMSM which includes harmonics, magnetic saturation, iron losses, optional thermal port:
