First check the Model Number and Serial Number stamped on the CPU and make sure it is the same numbers printed on the AMD Retail box on the white sticker sealing the box.
If it is different than someone switched your CPU but if it is the same than I have no explanation except maybe someone inspected the CPU before packing and sealing the box.
The White AMD Sticker sealing the box should be whole and not cut when you first received the AMD Retail box.
Also you can ask AMD Service Request (Official AMD SUPPORT) under "Warranty" if this is typical or if they believe someone tampered with your CPU before being shipped out. You can ask from here: https://www.amd.com/en/support/contact-email-form
AMD Support can probably check your CPU Serial Number to find out if it is used or new.