This is what I thought as well. Creaming butter and sugar properly gives the cookie better structure and spread less.
The butter also needs to be the right temperature before baking—chilling dough is sometimes needed. Also regularly scrapping the sides of the bowl while mixing is important to have a nice homogeneous cookie without gobs of dry flour or butter.
It’s possible you didn’t beat them enough, so there were large pockets of sugar, powder, flour, etc.
This is what I thought as well. Creaming butter and sugar properly gives the cookie better structure and spread less.
The butter also needs to be the right temperature before baking—chilling dough is sometimes needed. Also regularly scrapping the sides of the bowl while mixing is important to have a nice homogeneous cookie without gobs of dry flour or butter.
This is my guess too