I would imagine some of the FR pax may have got into departures which would (a big security no no btw nowadays) rendering the departure lounge and all pax within 'non sterile' requiring a departure lounge sweep and pax in it being re-screened ouch
I believe that is what is supposed to happen anyway. Sounds like a handling agent or airport worker left a door open sending pax down the departures route rather than thru the correct door thru arrivals route.....