Yes, but Lidl buys those and resells them. It's not like you can sign up with Lidl and pay 39 Euro/month to get a place in the cereal corner. The concept is a very different one.
A marketplace with sellers with third-party fulfillment is obviously different from a marketplace with no third-party fulfillment in a case about the fulfillment market.
The problem is that Lidl has the customer data which shows which products are most successful and it will compete with them.
Just like any other retailer, including Amazon.