just for the sake of info, it is illegal to retain fish that had not been caught by means other than what is described in the regulations. it is no different from the act of "gifting" or using a child with a toy fishing rod as an "active" fisherman to double your limit...the argument would be that the child can't be entitled to retain fish just because he/she has in their possession the tackle to show they were fishing...the parent would have to prove the child was capable of hooking and landing the fish or at the least be able to play and land the fish themself...so the key phrase would be "the act of catching and landing".
of course, in the case of the spey guy it's obvious he was more than capable of catching the steelhead, but if it was proven that he didn't catch and land the fish himself, he would be liable for breaking the law.