The aircraft doesnt automatically compensate by reducing thrust, the only immediate automatic reaction
AFAIK is compensating for the yaw by use of the rudder.
Although RUH is a pretty high airport, it isnt surrounded by any obstructions, the MFRH surrounding this airport is therefore 400 feet, i dont know what the MFRH BA uses, but it is possible that the aircraft transitioned from a takeoff attitude to an acceleration attitude which would resemble a loss of thrust due to the decrease in climb rate.
Cheers
Mutt.