That is weird; is there anything out of the ordinary mentioned in the listing where you bought the battery? The closest I can come is that it reminds me of those tag-on flex cables that are used to allow you to use a device programmer to reset the health information. But the thing is, those are only useful when you've transplanted your Battery Management System (BMS) from the original battery to a replacement cell, but that doesn't make a lot of sense in this situation.
Do you have a link to the listing for the battery? The form factor looks right for your phone; does it fit correctly in the case where it should? It's definitely not for anything like any of the iPhone 12 models, and for sure not the vanilla iPhone 11 either. Can you get a picture of the label on the battery near the top side so it's readable?