I don't know about Foster's so-called epiphany - but quoting the review:

Fishel said, "Some of those lyrics are very offensive today. But he came to realize that and went so far as to withhold songs from established artists like the Christy's Minstrels. ..."Foster said, 'Cut out these (offensive) songs or I won't give you any of my new material.'

Thanks Masato, those are nice sound clips.