Read the quote more carefully.
Quote Originally Posted by Alric View Post
Each State Party shall conduct risk assessments, as detailed in Articles 4 and 5, whether to grant authorizations for the transfer of conventional arms under the scope of this Treaty. State Parties shall apply Articles 3-5 consistently, taking into account all relevant information, including the nature and potential use of the items to be transferred and the verified end-user in the country of final destination.
Obviously there is a distinction between what is within the scope of the treaty and what a country decides is okay to trade from what is within the scope of the treaty. The U.N. would be deciding what can be traded. This measure also demands paper work with explanations concerning arms trade deals countries make. That puts pressure on countries to limit their options even further.

The sources I posted links to can help you understand the treaty better.