Rotational rate decreased when the legs deployed (see my earlier comment), but the angular momentum is still almost identical. That is the energy that needs dissipating. A little drag plus greater authority of the CG thrusters over the gridfins (getting less effective) got them there in the end. That's what I think. The CG thrusters should have the same moment available as long as they are fed with the same gas pressure, regardless of altitude, to a first-order approximation. Less mass due to fuel use during the landing burn probably factors into the equation somewhat also.