Why did hatter call Alice a him?

The Hatter calls Alice "him" as a playful reflection of the nonsensical and whimsical nature of Wonderland. This confusion aligns with the theme of identity and perception that runs throughout Lewis Carroll's "Alice's Adventures in Wonderland." The Hatter's misunderstanding emphasizes the absurdity of the world Alice finds herself in, where traditional rules of language and logic do not apply.