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.

- one of the biggest and earliest support of Emmanuel Macron, helped him become president (offering to do his PR, made him met the right persons -- especially Mimi Marchand, who can make and break celebrities, lawfully or not, helped set up Macron's political party with other billionaires, etc)

- control the #1 French newspaper, "Le Monde" (extremely poplar on the Web, too), is buying up other media (Nice-Matin, most recently), is/was also influential in opposition media (e.g Mediapart)

- his spouse is the first daughter of Bernard Arnault, the 3rd richest man in the world, and together they form the most powerful couple in the country

The only reference to Xavier Niel in this page is that he may have advised and eventually financially helped the french president Macron in his campaign. It is complete none sense that this would support the claim that Xavier Niel is evil.

In addition it's a pamphlet written by Juan Branco of all people, a nutcase conspiracy theorist who is more interested in self-promotion than any real social justice