Wondering if anyone knows what it means when a passenger is flagged on the computer system as a "protected passenger"?

A friend recently flew CDG-SFO on SE (XL Airways France). When the ticketing agent scanned his passport at check-in, a warning came up on her computer that said "passager protégé." She was very surprised and said she had never seen that message before. She tried a few things, but the system wouldn't let her proceed with check-in. She called several colleagues over, all of whom were equally baffled, until one entered some code that seemed to clear the flag. The original agent finished check-n, apparently having no idea of what that was all about.

Any ideas?