It's not at all "after hour" but only to preserve (remind of) the legal 11h break between workdays that is already in the law to avoid harming the employees health. The new catch is that it's an obligation for the employer to put some measures in place and define these hours. And you are right, it's not a law but the result of a negotiation (and not a violent one) between employees/employers unions
It leaves 13h a day 5 1/2 days a week for heavy workers to be connected : ~70 hours availability (max) paid 35... let's compare productivity now.
I know some journalists these days like to criticize France (mainly French ones, in France we are the world champ' on criticizing ourselves, look, I did it myself) but work habits, especially in IT, are not cool/lazy at all. French geeks like it long and dense like most geeks... Laws around innovation activities are quite interesting in France (less to no taxes and many public help), IT/science schools/universities are quite good as well, and the work market (the one I know, in IT) is still in favor of employees.