Was going to make the same comment. The entire BPS Space series of videos is excellent and goes into great detail on how it was done and the many challenges. To me, the BPS solution is also more interesting because it allows "throttling" (really variable deflection) of the solid rocket motor.
How did the guys in the OP do it? They used liquid fuel? I didn't know that was possible for model rockets
Looks like two separate motors to me. The second one is staged after apogee and is only powerful enough to slow the rocket down.
He described it in the video - he uses two motors. The launch motor is held in place by friction and is ejected by the ignition of the landing motor.