Indeed the article speaks to this:

“ In terms of washing, it should remove some residues on the skin of a product (which will often be fungicides used to prevent rotting during storage and transportation). However, many modern [synthetic] pesticides are what are called ‘systemic’ which means that they are absorbed into the plant and distributed throughout its tissues, reaching any fruits or flowers. As a result, pesticide residues are often contained within the body of the produce itself and therefore washing the surface won’t remove them.”