Export controls and sanctions are separate systems that overlap. Sanctions ask who you are dealing with; export controls ask what the item is, where it is going and what it will be used for. An item can be freely exportable to one country and licensable to its neighbour, and the same shipment can be lawful for a civil end user and prohibited for a military one.
Because the control attaches to the item rather than to a named party, screening a counterparty against a sanctions list does not discharge an export control obligation. That gap is the space in which third-country re-export and end-user fraud operate.