It looks like they're not leveraging LXC via Docker. I wonder if that's because they've been doing it this way pre-Docker, or if there are some technical reasons why it made sense to skip it.
Docker is great when it fits your use-case, but there are lots of practical ways in which LXC stands great all on it's own.
I've commented on HN before about why I often choose plain LXC over Docker: https://news.ycombinator.com/item?id=6378823
And also the lxc-user mailing list is a great resource: https://lists.sourceforge.net/lists/listinfo/lxc-users
It becomes more interesting when a) your system has been running long enough that you've learned operational and design lessons that justify an upgrade, or b) you're starting fresh on a new architecture.
Most of the Docker community is made of these groups A and B. If you're starting from scratch, or if making significant changes anyway, it makes a lot of sense to federate the development effort and reap the benefits of code reuse, common tools etc.