They signed a declaration of intent, not an agreement. On the other hand, if SA had equal interest to FC-31, China will not make it public, even an agreement would be very low key.
I am not saying SA is not serious with UK, they could be very serious. It could also be a typical bargain tactic to press China to allow FC-31's production line in SA (they asked for it). I think China is negative to the idea, SA is far less close to China than Pakistan and FC-31 is far more advanced than JF-17. Besides, China is balancing Iran and SA, selling FC-31 to SA is already a huge thing turning the balance, giving a production line is just too much. Essentially SA is pulling the same trick as Turkey in the SAM bidding except Turkey is not at odd with major partner of China in the region.
