Except you're measuring a population of France Télécom employees, not the average population of Normandie. Suicide may be high in Normandie because of unemployment, something that employees of France Télécom are not affacted by. Other things like educational achievement matter: e.g. in the US, "men and women aged ≥25 years with at least a college degree exhibited the lowest suicide rates" [0]. I don't have references for France but there are likely to be similar skews.

In this case there is a real question of if this is a clear phenomenon of workplace conditions induced suicide, as harassment, lack of proper training, and other poor conditions were widely reported, so while statistics are a useful tool they don't give all the pieces of the puzzle.

As a French person with family members who've worked at France Télécom, I can vouch that there are factors at play here involving perception of status and employment in French culture that may be novel to e.g. Americans. Japanese culture exhibits similar phenomena. The article summarizes it well:

“These companies were considered family,” Mr. Ledoux told the court. To be mistreated by one is extremely transgressive,” he said.

[0] https://www.ncbi.nlm.nih.gov/pubmed/28756896