Board Thread:Theories and Speculation/@comment-26904721-20150820181613/@comment-734582-20150823114308

GoldLiger wrote: The reason MN is a Senju Is that one guy deviates from everyone else, and so is assumed to be the status quo rather than what he really is, namely an exception to the rule.

We know nothing about Ashura. Maybe he simply was Kurama's jinchuriki. It's far more logical than assuming Minato, who has no senju connection, is a secret senju.