A 15-year-old student has had their hand blown off after picking up a stun grenade being used by police as mass school protests continue across France, local authorities said.
The incident comes as nearly 500 schools are expected to be completely or partially closed following student protests across the country over dilapidated schools and classrooms, overcrowding and teacher shortages preceding a nationwide day of demonstrations on Tuesday.


So, witnesses to the event say nobody picked it up, it just hit him that way and discharged facing his hand.
Edit to add this link (in French):
https://www.ici.fr/hauts-de-france/pas-de-calais-62/lens/blocage-des-lycees-un-eleve-d-un-lycee-de-lens-perd-une-main-arrachee-par-une-grenade-7395868
The same article says they haven’t officially determined if the student picked it up.