He his making a reference to a book published some times ago that was accusing a few french oligarch (which include Xavier Niel) to have basically put E. Macron

He his making a reference to a book published some times ago that was accusing a few french oligarch (which include Xavier Niel) to have basically put E. Macron in the Elysée. This book, that was also published around the time of the gilet jaune if I remember, made a lot of polemic, especially since his author is quite controversial and can be very vitriolic. A big issue with the book was that, even though some claim look legitimate and really not surprising for any French people (Macron being helped by a few powerful people was no surprise, he came out of nowhere and had suddenly more press coverage than any other candidate), it was also making a lot of heavy, and sometimes weird, accusation about some people, one of them being X. Niel, with nothing to back them up. It also didn't help that the author was writing in a way that really looked like he was settling some scores with people instead of actually doing a journalistic investigation (he seemed to especially bare some hatred toward X. Niel). It helped even less that he started beef with anyone criticizing his book, especially respected journalist and news outlet.