I don't know where you heard that, but I can guess why you heard that
The faster the coolant circulates, the less temperature difference there will be between the inlet and outlet. The coolant being returned to the engine will be warmer.
HOWEVER:
Because the flow is greater, the amount of heat being transferred to air by the radiator is greater, and the amount being removed from the engine is greater.
100 gallons of 150F coolant cools just as well as 50 gallons of 110F coolant in the same amount of time.
There is a loss, however. Heat likes to travel down a hill, and the steeper the hill, the better it travels. A point is reached where no matter how fast you circulate the coolant, the temperature is so close to the engine's temperature that not much heat moves. you won't see this effect in your civic or F150, however you might see this effect in an F1 or Indy car.