I'm mostly just inferring from the article. From the fifth paragraph:
At least in Europe people started to get way more thingy about what the Church called the “sins of the tongue” in the thirteenth and fourteenth centuries.
For the church to get thingy about sins of the tongue, the bible probably must be able to be interpreted in such a way as to prohibit them:
The north wind brings forth rain;
And a backbiting tongue, an angry countenance.
He who goes about as a gossip reveals secrets;
Therefore do not associate with a gossip
O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin. And do not spy or backbite each other. Would one of you like to eat the flesh of his brother when dead? You would detest it. And fear Allah; indeed, Allah is Accepting of repentance and Merciful.
It reminds me of usury — the texts of Christianity, Judaism, and Islam can be read to prohibit it, but whether it's read that way and whether the prohibition is enforced is a matter for religious officials.