I think Anonymous doesn't really know how DNS works. The root nameservers don't serve zone data for most sites that people use anyways.
DNS is a distributed hierarchy for serving requests. It's designed to be fault-tolerant because if every name resolution (google.com->8.8.8.8) performed by a browser had to reach 13 servers in the world, we'd still be using gopher and newsgroups instead of the web.
DNS is distributed, hierarchical, redundant, and cached all over the place as much as possible. Even my laptop caches DNS queries until a reboot. Even if a DNS cache misses (which is infrequent), it goes to the nameserver hosting the zone, which isn't a root name server.
Bottom line, it's probably just a joke designed to get some attention and to experiment and see what actually does happen if you hit those servers.