When the article first lists social animals, it gives a long list of "nice" animals (dolphins, dogs, birds, etc.), and then includes rats at the end of the list as though they were a disgusting afterthought, saying, "and even rats".
Later in the article the bias becomes even more pronounced:
"Dolphins, dogs and primates are the usual suspects when scientists talk about higher mental functions, but fairness, at least, extends even deeper into the lower animal kingdom. If you watch rats wrestle ..."Ever wondered how to push a biologist's buttons (or at least this one's)? Just say something like that.
The first error in this quote is the implication that there are "higher" and "lower" animals; this is evolutionarily inaccurate (for the same reasons that the evolutionary ladder idea contained in the TTLB ecosystem rankings is incorrect).
Making things even worse, the author includes rats in the list of "lower" animals. While it is possible to argue that some animals are more complex than others on a gross morphological level (e.g., humans are more complex than sponges), attempting to place rats in a category of "lower" animals (compared with humans) is ridiculous, especially given that the author has included dolphins and dogs as "higher" animals.
The problem with labeling rats, but not dogs and dolphins, as "lower" animals is that rats are evolutionarily closer to primates (and thus humans) than dogs and dolphins are. As you can see in this wikipedia entry summarizing molecular-genetic work on mammals, both rodents and primates can be grouped into superorder Euarchontoglires (wikipedia page), while Carnivora (including dogs) and Cetacea (including dolphins) can be grouped into superorder Laurasiatheria, an equivalent lineage to Euarchontoglires.
So, if you're going to assume that the evolutionary ladder idea is correct and argue that animals close to humans are "higher" and all other animals are "lower", since rats are more closely related to humans than dogs and dolphins, you can't simultaneously argue that dogs and dolphins are "higher" animals while stating that rats are "lower" animals.
What we're really seeing here is the common misperception that rats are just red-eyed, blood-hungry vermin whose only function in this world is to spread horrible diseases and make 1950's housewives shriek from the tops of tables. Domesticated rats and mice make exceptionally good pets, are probably less dangerous than your average dog or cat, have very human-like behaviors, and are cuter than cuteness itself (see my baby mouse photo archive for evidence). Wild rats and mice are just like any other animals trying to fend for themselves.
And yes, based on the molecular evidence I described above, rats and mice are more closely related evolutionarily to humans than either cats or dogs (or horses, dolphins, aardvarks, birds, lizards, sea anemones, or nematodes, either). Get used to it.