I find it concerning when the pilots' "misunderstanding" (by both crews) is given as the "cause" when the root cause was 2 aircraft at the same FL on a converging course. The "RT was clearly stated on the VHF recording" which I suspect means a recording of what was being transmitted, prior to it going over the airwaves, maybe not clearly received, maybe blocked by Box 2 or I/c or Cabin chit chat etc.
SOPs likely permit at that stage only 1 pilot on the Flight Deck, maybe using speakers / microphone, when compared to busier climb/decent phases.
As there were two 'avoiding action' instructions close together I think the first PF didn't fully hear them picked up half the second heading and thought it was a repeat of the instruction to his aircraft
I think you are correct... when ATC order a Go Around it is "C/S Go Around I repeat Go Around", no doubt with good reason...