They are not before and after shots. These are both "after" shots, the first one of the inbox view and the second one of an email view. Click on the image to see the default gmail view for comparison.
I guess GP meant those before and after screenshots. I agree with them in that I also don't what the difference is. I also never used Inbox for more than 10 min. It's the same, just a bit "prettier" with the definition of "pretty" being "bigger and with more whitespace", which I don't necessarily agree with, at least for email.