a key phrase in the article might be: "Dixon's genius as a songwriter, lay in refurbishing archaic Southern motifs, in contemporary arrangements"
which seems to leave his songwriting open to interpretation a tad, but so
far I've found nothing to indicate his having claimed unearned credit for any
of his songs.
for example, "My Babe" is "This train is bound for Glory" but I don't beleive that puts Willie Dixon's song writing abilities into question.