It is the same site, but I changed the domain name in late May, after Penguin had decimated my traffic. There had been no significant hosting, tech or site layout changes for probably at least a year before Penguin hit me. I had actually wanted to change the domain name for years, but didn't want to risk hurting my Google rankings. Once Google took the rankings away anyway, I figured no time like the present.
Now, in that same spirit, I've made a LOT of changes post-Penguin - deleting pages, re-organizing content, etc. I knew Google might react badly to all that, but these were changes I felt would please users, and going by the social media response to the site, I was right. So it's possible these changes caused the August 23 even-further-plummet. But not the initial Penguin drop.
On a side note, I'm pretty philosophical about this whole thing. I'm really curious why this has happened, but it doesn't really matter to me. For a while now, I've been operating on the assumption that my Google traffic would suddenly disappear one day, and positioning my sites to survive that. This experience has allowed me to test my theories about getting past a big Google drop. Now I know precisely what happens, and that I can survive it if I have to. I'd love the Google traffic to come back, of course, but que sera sera.