Firstlly, invite your colleague to attend! Secondly thanks for asking, I wonder how the choice of model here is justified in real life then. in the text its just stated we will use OLS, I wonder if this is just commonly accepted or if there are common alternatives
It can be any model. OLS is the more traditional/conventional way. I believe, since these causal inference techniques originated mostly from econometrics and not, say, AI practitioners, OLS has traditionally been used.