I mean, maybe Brown really didn't know, and was just expressing the fact that he was unsure whether Obama's mother was married. But why would that possibility even be in his head? I took a little tour of the wingnuttosphere to find out who'd been saying what on that topic.

Turns out that a number of fringey folks, including one Andy Martin and prominent wingnut Jerome Corsi (of "Unfit for Command" fame) have been assiduously peddling the theory that Ann Dunham and Barack Obama, Sr. never actually got married. Said Martin, in July of 2008 (not long before Brown taped the interview posted above):

Barack Obama, Senior, and Anne Dunham never married. Obama knows this fact. This is also why he keeps his white grandmother a virtual prisoner; she knows too, and she won't lie.
Through the past several decades Obama has pretended he 'didn't know' the facts about his illegitimate birth. He thought he could get away with the big lie. And he almost did get away with it....

His mother was promiscuous and had a child out of wedlock, in 1961, when that was still scandalous behavior. Is this Obama's idea of 'family values?' Obviously, he has been deceiving the American people and hoping his advertising lies could overcome the truth. He has failed.

Corsi, for his part, has been keeping the faith even post-election. This post at World Net Daily, "Was Obama's birth out of wedlock?", is from September of 2009:

Was President Obama born out of wedlock in 1961? ... As WND has previously reported, the only documentation for Ann Dunham's marriage to Barack Obama, Sr., comes from their divorce documents that list the marriage date as Feb. 2, 1961.... No wedding certificate or photograph of a ceremony for Ann Dunham and Barack Obama Sr. has ever been found or published.