That's what National Geographic says, in the last paragraph of a new article: "It may well be the first western European city with a majority of its residents from Muslim backgrounds."
Probably better for the magazine to have said it may be the first majority Muslim city in western Europe in about 700 years. If I recall my history correctly, in the 13th century, many western European cities, such Granada and Cordoba, were majority Muslim. I remember being told that Cordoba (AKA Qurtuba) was at one point the world's largest city and had 3,000 mosques. Not long before that, the entire island of Sicily was an Arab emirate. Dunno if it ever was majority Muslim, but I'd bet Palermo was.
(HT to Al D.)