I really can't say what they were hitting not being there and all. Other than some type of emerging bug of course. In this case, instead of focusing on what they were hitting...work on what can I make them eat.
Near surface risers are almost always eating emergers. So, I carry an assortment of soft hackle wet flies in sizes from #12 - #24. Color is normally not as important as sizes, so pick a color like gray or brown and tie a few soft hackles in each size, all in the same color.
Start with your larger softies, and size down until you find the size they like. Fish your soft hackles by casting past the rise forms. Then swing the fly in front of their location. You can mix up the retrieve to adjust to water speed and what the fish are into. Sometimes a lazy swing, some time short quick strips, some times long slow strips. Just mix it up and you'll find what they like.