diberry - 5:01 am on Jun 8, 2013 (gmt 0)
I would say that this is not Penguin. I have done no link building at all. In fact, the website has less than 20-30 or so back links and they are all organic.
Actually, Penguin has hit at least a few sites with clean backlink profiles like yours. If you took a hit on May 22, it's almost definitely Penguin. We don't fully understand Penguin - Google has said we'll never backward engineer it - but a spammy backlink profile is definitely not required for Penguin to affect a site.