@sid Did you improve the content or did you add a few lines of text? The two aren't always the same! ;)
@JS I saw something slightly different. I followed the same process - went through the site and removed content I felt wasn't good enough. The site recovered after that.
I think there is a degree of relevance needed with content - the pages I removed were all optimised and ranking for terms, but didn't really say much. "Thin content". Essentially they ranked for "product" terms but didn't actually sell the product. If this is the case with your friend, then slightly adjusting the focus of the content to informational queries might actually make the pages more relevant for slightly different terms, hence the recovery.
I don't think there's a technical fix for Panda there. It's not the case where you can say "I need to do x, y or z". It seems very subjective - particularly considering it surrounds the idea of quality and most people have different ideas of what this means.
There was a time when many people in the industry would describe "quality content" as being original / non-duplicate content. Indeed, many may still believe this.