Bearing in mind the number of young French people who supposedly had a "favourable or very favourable" opinion of ISIS vastly exceeded the number of young French people who were Muslim, I suspect it had little to do with religion and everything to do with a particularly poorly phrased French version of the question....

The polling organisation is reputable, but the detail that they and the Russian state media organisation they conducted it for provided is scant: http://www.icmunlimited.com/media-centre/press/isis-poll-for...

Similar polls of almost-exclusively Muslim, mainly Sunni and generally anti-West Gaza have found a much more negative opinions of ISIS