ZydoSEO - 5:20 pm on Jan 26, 2013 (gmt 0)
I've seen this phenomenon before on a huge online education site. Their situation started in the late 2010 timeframe and slowly, progressively got worse over time. After digging deeply into their analytics, what I found was that their degree pages were previously ranking for tons of "loosely relevant" phrases which had been driving a lot of (non-converting) traffic to their pages.
For example, a Masters in Computer Science degree page might have been previously getting traffic for loosely related keywords like "computer programmer", "computer jobs", "data structures", etc. While these terms are loosely related, they rarely converted for this client. Much of the traffic lost in this situation was for phrases such as these.
Personally, I think this is often times the result of Google changing how they detect user intent. As this has changed drastically over the last couple of years, in a lot of cases they have stopped sending traffic to pages they probably never should have been sending them to in the first place.
I would say forget about Panda and any corelation you might attempt to draw from "not" having been hit by it. It could be a situation similar to the one I described above or it could be that whatever led to your issues is preventing Panda from even coming into play. I would be looking at a lot of other things like those that jimbeetle suggested and more.