Shopify suggests products on the product page based on sales results. Your “delivery” product will be most probably one of the hit products as its always both with every order were pick-up point is used.
You should enhance suggestion functionality to endure Parcely product not to appear in product suggestions. If you are not selling thousands of products then we would suggest a simple app that allows you to manually add all suggestions for each product. By adding suggestions manually you can also make suggested products become more logical for customers. There are many app’s in Shopify app store which offer even free plans. We have priviously used Globo for example.