Well, both of those articles explain that this was just perceived as a dissonant interval which could be used a a musical representation of the Devil. The interval was likely avoided for essentially aesthetic musical reasons, and the Wikipedia article says that "...suggestions that singers were excommunicated or otherwise punished by the Church for invoking this interval are likely fanciful." Unfortunately the BBC article seems to be light on facts and heavy on stereotypes of medieval monks as ignorant religious fundamentalists.