In this case that food is probably not cows milk, typically being pasteurized before being sold. This is not a debate about macronutrition, it's a debate about the particular distributions of guy bacteria in different people
I dont think the commenter is saying that they are lacking the bacteria. If they have a bacteria that feeds on lactose / milk, and they give pasteurized milk, ,it will promote growth of that bacteria.
Only if they dont have the bacteria at all would pasteurized made a difference.
But it's not even clear that the bacteria feeds on the milk. There could be other mechanisms of action for preventing or suppressing allergy.