I'm not an expert or science guy, but I would also think that fishing pressure, and the current habit, may have something to do with the motivation for striking a fly.
Case in point, in addition to fly fishing, I fish bass tournaments. In the spring, they spawn. If I cast a plastic lizard near a bed with a spawned female on it, she we will likely strike it out of defense, not necessarily out of hunger, in fact, sometimes they will just push it off the bed before I can even set a hook on them. Also, I've heard that sometimes fish will hit something unfamiliar just to see what it is.
Now, take Manchester hole, choked with fish, and massive amounts of anglers casting to them day in and day out, and the fish have very few places to hide. Being so skittish, the only defense they really have is to shut down and not eat anything, and avoid everything drifted in front of them like the plague. But, that of course isn't going to keep anglers from continuing throwing every fly in the box at them. However, if you cast to a fish many times, eventually you can get it to strike. I've heard the theory that this happens because the fish strikes out of frustration, and may just want the fly to leave it alone. This seems somewhat plausable to me.
However, I would not consider it to be much of a reaction strike if the fish follows the fly for a few feet before taking it, as was the case for the fish that took the mouse. To me, a reaction strike would be more of the fish whacking the fly the second it sees it, or the second it hits the water, sort of an impulse. For example, last time I was up, was fishing a pod with one other guy. Was doing pretty well, however, there was one fish I continued to observe. About every ten minutes, it would come up and gulp on the surface, as if taking an emerger. Saw some fish moving up and settling in the lower section of the pool, so decided to toss my glo bug into the pod. Sure enough, this same fly twice came up and whacked my orange indicator, almost as soon as it hit the water. I remember reading somewhere the theory that this could be an instinct reaction of the fish, installed by the pellets they are fed in the hatchery.
Again, I could be wrong, not saying I'm an expert on the philosophy of a steelhead's behavior, just some reasonable theories. Not knocking anyone's catch. In the end, if you manage to have a trophy fish take your fly, and land it, who cares why it hit.