I can't speak about the site in question, but I'll give you the benefit of my personal experience: New sites sometimes get weird PR. My site had a PR 8 for a month... Now it's up and down between 4 and 5.
I don't think it's particularly unusual for a site with solid PR 7 links and a couple PR 6 to have a PR of 6. In fact, I have seen just 1 PR 7 link give a PR of 7! One PR 7 link is worth hundreds of PR 4 links.