Looks like it is supposed to be a Lemming, as they refer to it on their github page (4th bullet comment). But I don't think they actually give it a name.
Also, fun fact, (and trigger warning) the Lemmy logo isn't symmetrical.
About the name: Wikipedia: Like many other rodents, lemmings have periodic population booms and then disperse in all directions, seeking food and shelter their natural habitats cannot provide. The Norway lemming and brown lemming are two of the few vertebrates which reproduce so quickly that their population fluctuations are chaotic, rather than following linear growth to a carrying capacity or regular oscillations. Why lemming populations fluctuate with such great variance roughly every four years, before numbers drop to near extinction, is not known.