game wardens are state or local officials responsible for enforcing laws pertaining to the hunting, fishing, and trapping of wild animals. (Wikipedia)
to be casual: The speaker wanted to know where he could find the famous fish without alerting the listener to his intent. The term 'act casual' refers to the attemt to send a message with one's body language that differs from the individuals situational reality. A boy asking a girl for a date would want to seem calm and relaxed, especially if he were very nervous.
a mountain feud: I beleive this is a cultural reference to the famous Hatfield-McCoy feud (1878 – 1891) an account of American lore that has become a metaphor for bitterly feuding rival parties in general. It involved two warring families of the West Virginia-Kentucky backcountry along the Tug Fork River, off the Big Sandy River. (also Wikipedia) Their private war totaled 7 murders and by the time it was over no one could remember why the fighting began.