A yordle can be a child as well.
I suppose that he is a yordle, but he doesnt remembers... so, it makes sense for him to think that he is a human, that had a human family in the past.
Why do i think that he is a yordle?
Because of the 3 stories and something from "Greed and Tears".
“The walls inside were smooth obsidian and carved with ancient writings and images. He could not read – he was a simple man – but he studied the images.
“He saw a boy prince, sitting cross-legged upon a sun disk borne by a team of servants, a beaming smile upon his face. Chests of coins and riches were piled before him, the offerings of strangely garbed, bowing emissaries.
“He saw other carvings, again showing the smiling prince, this time walking among his people. Their heads were pressed to the ground before him. Stylized rays of sunshine radiated from the boy’s crown.
This is the only thing about the Amumu lore that we know that is true for sure, because the rest of the stories are legends...and the images that the man saw are real.
According to the images, Amumu was an emperor, as all the legends tell... however, there is one image that fits with only 1 legend: The image that show "the smiling prince, this time walking among his people. Their heads were pressed to the ground before him. "
And that legend is the legend that says that he was a yorlde:
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 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.