Is sexist behaviour always grounds for dismissal?

Mr. [S] was hired as a senior technician on September 21, 1993 by the public technical and industrial establishment Commissariat à l’énergie atomique et aux énergies alternatives (CEA).

On September 1, 2016, he was given a precautionary layoff and summoned to an interview prior to possible dismissal, then to appear before the conventional council, to which the employer submitted a proposal for a one-month layoff.