Honestly, I did not find any faults in this example. Look at it this way:

Even if someone gets milk from online, they would still have to utilize an online store. Shopping online is still going to the store in some way. Going to the store is sufficient for buying milk because you can get more than one thing besides milk from the store, or you may not even buy milk at all. However, in order to buy milk, you MUST go to the store, whether that'll be in person or online.

Wonderful lesson!!