There seems to be a confusion here:

Amylose is a polysaccharide and one of the two compounds that form starch (alongside amylopectin). What Oatly adds is amylase, one of the enzymes in our body that breaks down polysaccharides into absorbable sugars which means that their oat milk already contains higher amounts of reduced sugars due to that process which is shown in the study I’ve linked earlier.