Note that the list of associated users is for forum accounts here on the community forum. It enables access to the customer forums. It doesn't have anything to do with downloading xenForo from the customer area.
Adding forum accounts to your customer account is just to enable those members to have full access to all the customer forums. It is not to allow them to download and install a copy of the software.
As per the license agreement, you are limited to 1 normal installation and 1 test installation: You may create a single additional test installation for the purpose of testing the Software. Any test installation of this kind must be password protected, and access to it must be limited to You and Your website staff.