I presume it’s a lemming. The page where the Lemmy code is posted has a section:

Why’s it called Lemmy?

• Lead singer from Motörhead.
• The old school video game.
• The Koopa from Super Mario.
• The furry rodents.

Which mentions lemmings twice (the rodent and the game about the rodent). I’m not convinced it looks any more like a lemming than our one.