Normal
It depends on your case airflow. Sometimes it is better to supply the radiator with fresh air from outside the case. For example, Corsair states: "For best cooling performance, we recommend mounting the fan as an air intake to your PC case." If you have a GPU that is dumping hot air inside the case, then supplying cooler outside air to the radiator could perform better than pushing warmer air through the radiator as exhaust. Bitwit and Optimum Tech both have good videos comparing intake/exhaust and radiator orientation that demonstrate some counter-intuitive results. Again, it really depends on orientation, and available airflow paths in your particular case.
