The safety car was coming in that lap, and he has to make a gap before the restart. His engineer had already warned him that the previous restart was very close. The rules clearly state that when the safety car is coming in the lead driver controls the pace and is allowed to create a gap greater than 10 car lengths to allow the lead driver to restart the race without overtaking the safety car before it enters the pit lane.
Could you please share the telemetry you have that shows Hamilton braked and was doing 49km/h? To quote such specific numbers suggests you have the telemetry for the car, so please share it so we can shut down this discussion and prove without a doubt that Hamilton was at fault as you say.