I really have no way of knowing what went on for you between the bugger fishing and the dry flies, but I have noticed the following in my own fishing and it may have a parallel in what you're observing with your casting.
Most of us love to fish dries. They're visible, which makes the fishing fun, and they're easy to cast. But, unless you have a lot of line out, you don't get a whole lot of feedback from casting dries; because there's practically no weight on the end of the tippet to signal you the difference between a good cast and not-so-good cast.
I found that fishing heavier flies (buggers, muddlers, zonkers, etc.) helped me a lot in developing a reasonable cast. When a big bugger turns over on either the backcast or the forward cast, you can feel it through the line and the rod (there's a definite jerk on the line). That's the feedback that I'm talking about. If you're frequently casting buggers or heavier flies, then you're going to be making a series of adjustments/corrections to your cast in order to get a decent cast with the heavier fly on the end of your tippet. If you do that enough times, those adjustments/corrections will become part of your normal casting motion, and that will translate into casting better with almost all flies; particularly dries.
Another thing that has helped my cast is fishing with sinking tip lines. Whether it's an intermediate tip line, a 150 grain (heavier) or a 250 grain (heavier still) line (I don't fish heavier that 250 grain unless I'm fishing saltwater), the feel that you get from that heavier line gives you a lot of feedback that, I think, helps with your cast.
On the other side of the equation; the rod side, as opposed to the line side (which includes the fly), if you fish with a slower action rod instead of a fast action rod, you'll also get a lot more feedback, because tip-flex rods don't deliver that much feedback (at least they don't for me). Joni recommended a 7'6" Eagle Claw 6 wt/ fiberglass rod to me a couple of years ago and I still practice with that rod. It cost $16.00! It's a very slow action rod (some would call it a noodle), but if you can throw a good tight loop with that rod and get good distance at the same time (and you can), then when you go back to a fast action graphite rod, the results will very likely show an improvement in your casting.
Glad to hear that your casting is improving for you.