Quite simply that enforcement officer was wrong.

Remember when the Game dept had the rule you could not carry a modern handgun while muzzy or bow hunting? That got changed because they where not in compliance with the RCW.
The game dept. cannot set their own rule regarding firearm carried for self defense.
This is a pre-empted state. Only the legislature can write new gun laws regarding carry.
Game agents and many LEO are simply not that we'll informed.