The right to detain someone usually includes probable cause of a violation being committed. If the guy was cooking and using the park in a manner that complied with park policy and regulations there is no probable cause. Unless the Officer had ESP or open carry was involved then how did he know he had a permit? The officer was just fishing...
There is no because I am a law enforcement can detain you because I want to right that I am aware of.
The guy was right in pursuing this. Now hopefully the departments will include this in regular training.
Have a nice day at the range
NRA Life Member