Paul, Of course fish anywhere can be selective. Selectivity is usually a function of either a super abundant food item the fish imprint on to the exclusion of all others, and or because of excessive angling pressure. Also, there will always be unexplained examples of selectivity only the fish know the reasons for. But in general terms mountain trout, whether they live in lakes or streams, will not be all that selective because those waters offer so little food for the fish to eat that they are generally forced to take what ever they can get, which is the reason why those anglers that stick to the One-Fly-Only-Pattern doctrine do as well as they do. And I see no good reasons why they should not do well on streams with that concept. Lakes, however, are a little different, as you have found out. That is not to say that certain fly patterns or sizes of fly patterns or lures will not work better than others. One classic example I can give you of this is midge feeding trout, where the surface looks like a light rain is falling on its surface. Most anglers confronted with this situation automatically think the fish are taking dry flies, and mount the same on their leaders, casting for as long as the action lasts with out getting a single bump. When the trout are taking midge pupa just under the film, it really pays to throw midge pupa patterns at them. When I did my pattern tests in 2010, catching and releasing 1,339 fish over 31 angling days, I changed patterns every 10 fish and noticed no big fall off in productivity. But if the fish were feeding on the midges, I stayed with midge pupa or emerger patterns as long as the fish continued to feed on midges. Sure some colors and sizes did better than others did but I never fished a pattern that was a complete failure unless I went outside of the trout's desired insect species preference.
Likewise, when the wind came up and the trout switched to taking terrestrial insects, I switched to terrestrial fly patterns as well. Changing patterns after every 10 fish, from ants to beetles, to hoppers to spiders, from size 12s to as small as size 18s, and again while some patterns and sizes undoubtedly worked better than others, I never failed to catch at least some fish on any terrestrial fly pattern that I tried.
The midge emergence is temperature dependent, and once the air and water gets above a certain level the bug and fish activity shuts down. The terrestrial insects are deposited into the water by thermal winds, usually in the afternoons. The time between when the midges quit and the land based insects begin to fall into the water is usually a dead period of time for the fish and the fishing. But the Sheeps Creek patterns turned that unproductive period into a productive time for me, much more so than fishing with my more standard patterns, such as the Hare's Ear and Pheasant Tail nymphs, the Timberline Emerger and such fly patterns, to the tune of 650 fish caught and released that season on the Sheeps Creek fly patterns, again changing patterns and sizes every 10 fish. Any fish can be selective at ay time, but mountain trout do not exhibit selectivity to the same degree that spring creek trout on heavily fished waters do. Still, you have to do the best you can with the hand you are dealt. And it sounds like you did just fine in the situation you were given. You can't ask for any more than that. I wish I always did as well as you did on the trip you spoke of.