Not [U]necessarily[U] true in fact.
If there is little or no airflow over the brakes then releasing the park brake can, in fact, reduce the rate of cooling, as the gap between the discs is tiny and heat is simply radiated across the gap from disc to pad (and v.v)
By leaving the park brake set the heat can be transfered and radiated (away) through the whole assembly.
BUT......
If you have a suitable breeze and especially if you are using brake fans then the better option is to have the park brake off. The airflow being sufficient to pass between the pads/disc and draw heat away (and cooler air in).
The actually difference in cooling times (no fans) with the park brake on or off is actually quite minimal anyway.
Having said that it may still be a significant factor for LCCs with their rapid turnarounds...I dont know?
Chocks? Complete red-herring.
The brakes will continue to heat up for several minutes after landing...its normal as TC notes above.