Is Amumu a yordle

In his updated lore, it's purposefully left open to interpretation. In the past he's been both a Yordle and a young boy, so Riot preserved both with the update

Yes, in the lore he used to be a little kid but now he's a yordle

Race Undead (Formerly Yordle) http://leagueoflegends.wikia.com/wiki/Amumu

"Yet another story of Amumu tells of the first and last Yordle ruler of Shurima, who believed in the innate goodness of the human heart. To prove his detractors wrong, he swore an oath to live as a beggar until he made one true friend, convinced his people would rally to help their fellow Shuriman.

Though thousands walked by the disheveled Yordle, not one stopped to offer a helping hand. Amumu's Despair.png sadness grew until he eventually died of a broken heart. But his death was not the end, for some swear the Yordle still wanders the desert, forever searching for someone who might restore his faith in humanity."