That definition is archaic
Note the 1901 date. The term "concentration camp" has taken on a far more evil conotation since the Nazis. Whatever is happening in Guantanamo it's not evil. Sure these would-be-mass-murderers are being grilled daily and it's no carribean vacation they're on, but there is no torture or murder happening there. If you want to call it a concentration camp then go ahead but what's happening there are not atrocities.