Andy Miller told The Associated Press on Thursday it wasn't clear there was even a provision in Livestrong's bylaws to ask the founder to leave.
Armstrong resigned as chairman in October shortly after a report detailed his use of the banned drugs.
Armstrong told Oprah Winfrey earlier this year he wasn't "told to leave" but was aware of "pressure."
Miller says the board was abuzz over the scandal at the time and that may have given Armstrong a sense of being pressured.
But Miller says, "It ultimately had to be his decision."