This point is actually acknowledged in the study findings under "Strengths and Limitations":

A limitation is that the information we collected did not allow us to separate educational screen time from other types of screen time. Doing so may have helped us in examining the association between screen time and child development while considering both positive and negative aspects of screen time.

The original data used in the study did not allow this differentiation but these findings can be used as a starting point for further research.