Well, the singer in question said that France was a country of "kuffars" in one of his song, which is the arabic for "misbeliever" in a pejorative manner. Which shouldn't be taken seriously though, because as far as I know, the rapper (Which is hardly a rapper, he's just a popular artist that makes songs for teenagers) in question is neither muslim nor of arabic ascendency.
I despise the far right, but it was quite inappropriate to let him sing for the commemoration of World War I, unless he would have sung about world war I, which I doubt.