If you are listing products with EAN numbers that are already in the eBay catalogue, then they will pick up information that is already on the eBay catalogue - such as Item Specifics, eBay Categories, and more.

But sometimes not everything that is in the eBay catalogue is correct.  Here is where the Opt-out option comes into play. 

Using the opt-out tickbox located on the product edit screen, you are able to unlink your listing from the eBay catalogue, meaning that you decide in which category you would like to list a product. 

You can find the opt-out option when editing a product next to the EPID and EAN fields: