I think that is a natural reaction Ed, or at least nature doing its thing. In Michigan the Betsie river has a natural run of Kings and as far as I know there has never been a stocking plan or release for that river. I have fished there since the beginning of the 70's.
Yes... straying is a built-in life strategy for salmonids to colonize other streams. Literally not putting all their eggs in one basket.
Although I wouldn't call it straying once they enter their natal river system. You can characterize straying/homing at different spatial scales (as precise as homing back to the exact redd a wild fish was born in, or as large as an entire watershed), but typically we're talking about getting fish back to the same individual river system they were stocked in.
Generally when we're talking straying, it's fish entering a different river system than they were stocked in. E.G. if we got a Trail Creek fish in the Little Cal, I would call that straying. But not a Little Cal fish in the West vs East Branch.
Once they enter their natal trib, all bets are off. West Branch and Salt Creek get salmon despite stockings on the East Branch. Some go right, some go left. If there's enough water, they'll keep going up into drainage ditches. Same in Trail Creek, once they are in Trail, some go up Cheney Run, some go up the West Branch vs the East Branch, some go up Waterford Creek, some go up Wolf Run, etc.
Same in the Grand, the St. Joe, Muskegon, etc - basically any system in the Great Lakes, all the tribs and branches of salmonid streams tend to get runs
