> What would you predict are the amount of people total who bought almond milk instead of semi-skimmed?

Likely a large amount of people about to or becoming obsessed with fitness, or vegan recipes. The problem here is that all those "milk alternatives" have absolutely nothing to do with milk whatsoever, they have different handling and nutritional value (or lack of it; to the detriment of innocent kids suffering their parents' obsession). For most people, using the word "milk" will pull all kinds of wrong associations from their minds' latent spaces, which they won't be able to evaluate and ignore.