"If this occured at low altitude at a point of low thrust the engines may have gone to ground idle instead of flight idle therefore needing around 8 secs to wind up again."
I also believe that ground idle would contribute to this, however ground idle generally requires ground shift - ie - weight on the gear struts, wheel spinup, ect. . . . It's not unheard of however, for an in-flight aircraft to be in ground mode.