Please Goto SPRO-> Logistics General->Basic Data Retail-> Distribution Chain Control. There select the respective Distribution Chain and choose Details.
Under the Control Submenu you will notice Dist.Chain Category there select the option 1 - Distribution Chain for Stores.
I think the answer of Madhan Raj is the correct answer to your question. Can you confirm that? Also, the create customer screen I believe appears when you are trying to create a Store site. It is because if it is a store then it sure will be a customer in the future (it is a customer from the Distribution Center's point of view).
Here is the link of the thread that had the same question as you: Creation of a site..