Emotional, psychotic loyalty, psychotic no knowledge, ambition, actually won, no knowledgeWhy would Hinata challenge Pain?
Or Jugo challenging 4th Raikage, Dosu challenge Gaara?, suigetsu challenging Kisame, Karin attacking Guru Guru Yamato Buddha statue, Kakuzu attacking hashirama.... Etc Etc..
Look at context, please. Mifune has previously fought Hanzo, even putting aside his known hype. He wouldn't challenge someone who is outright above him.