The charge was blasphemy, or, in the words used in the article: "disparagement of religious precepts". It could not be defamation because there is plenty of evidence that Muhammad did marry and have sex with a child. That was not doubted even within the Muslim community until it became a source of controversy in modern times.

With Ireland's recent repeal, it seems there are now only 17 European countries with blasphemy laws, including Austria, where this case happened:

> Andorra, Austria, Cyprus, Finland, Germany, Greece, Italy, Liechtenstein, Poland, Portugal, the Russian Federation, San Marino, Spain, Switzerland, Turkey, the United Kingdom (Northern Ireland and Scotland) and the Vatican City. This list excluded countries like Belgium and Luxembourg, which provide narrower provisions for insulting the objects of a religion in places of worship or public ceremonies.

https://ipi.media/despite-danish-repeal-blasphemy-laws-still...