I have been reading the thread since the very beginning and, my two cents, when (the Captain) says "don't worry don't worry" at 3.600' he may be referring to the GA final altitude (3240') overshooting by 250'. It is true that in a high thrust and light weight situation an altitude boost is not that uncommon but maybe this GA altitude boost, if such, may point to a possible AP/trim/FD malfunction that lead to the subsequent pitch down.
What can be hear next is: "don't do that don't do that". Whose voice is it? Is it the same voice as in "don't worry"? If so, we can assume it was the Captain who was flying the GA and then asking the FO not to do something specific when he felt something was off. I'm not a Boeing guy, closest I flew to Boeing was MD80, so here is my question: is there any SOP (Boeing or Fly Dubai) that involves two pilots manipulating the flight controls or surfaces at the same time?
Also, what is the SOP in FD when in GA? Accelerate at final GA altitude or at the standard 1.500' AGL or 3.000' AGL when in noise abatement? If they were planning to level off at final GA altitude (3240') after accelerating at 3000' the flight automation might have acquired the final GA altitude way early (IF it is a function of the v/s during climb, as it usually is, but I am not a Boeing guy), if the FO in that moment cleans up the airplane - without waiting for the Captain command - with a lower than required speed for cleaning, is there any kind of protection in the 737 that could have triggered the nose down moment? Is that why the Captain says: "don't do that?", because the FO retracted the flap below the minimum speed?
Does it make any sense what I'm saying here?