I think you are right about everyone flocking to the DSR yesterday. You got lucky!
We tried a similar experiment on the fish in the fly zone. We'd watch a fly being drifted through the fish and they would all get out of the way. Don't know if this is from the pounding they take on a daily basis or their general inclination to shy away from a fly when they get that far upriver (stale). Either way - no one is going to catch them legally when they are like that....so are the crowds just fooling themselves about "catching" fish when they are in fact lining them? Seems kind of sketchy to me.
Last year a friend and I stood and watched 2 off-duty guides snag fish after fish and play them all the way in. Kinda says something about the legitimacy of the upriver salmon fishery.
That said, we had a very fun day yesterday AM with agressive fish (cohos mixed in). Have also stumbled across good numbers of fresh steelhead on occasion which make for unforgettable fishing days. I'll be back - just not for the salmon run.