Machinbird
The roll oscillation finally stabilizing was likely related to the decrease in roll acceleration available as a result of the substantial deceleration that the aircraft had experienced as was approaching stall speed.
Not sure about that. I take your point that system gain (roll acceleration/stick movement) was reduced as the airspeed fell, but against that you have to set worsening dutch roll damping and increased roll/sideslip ratio as AOA increases. And I don't think one can exclude Bonin learning how to fly it!