Wow, you really did your homework. Yours is perhaps the most instructive Panda-recovery anecdote I've read to date. Tell us: did you revise you META descriptions as well, so that searchers are more likely to click through to your site based on the SERP squib?
With reworked content that more completely provides the information (or "answer") your long-tail searchers seek, what is the typical reader's next action? Is the reader less likely to bounce back to the G search results? Is the reader spending more time on the page and then browsing your site further. If Google Analytics knows as much, then I suppose it makes sense that your editorial labours have paid off. Is this what you speculate is going on? And if so, isn't running Analytics and implementing similar changes a really good idea for anyone seeking to recover from Panda?