Really interesting read this, I am an ATCO, ex Dubai, currently Gatwick Approach.
My ATC perspective is controller error caused by a missed read back. Yep the passing of traffic information was good and should of enabled the crews to form a mental picture of the traffic situation and re-affirm their clearances. However that is not their job, unfortunately mistakes happen, and this is what this was.
Controllers leaning point, listen to read backs. Pilots learning point, try and be aware of the traffic picture, and if doubt question your clearance.
Am sure the ATCO will be beating himself up over this, in the end it was his error.