No, it means that about 50% of people scanned would trigger a "positive". The false positive rate is the number of false positives divided by the number of actual negatives.
100 people, 50 false alarms, 1 actual problem alerted and 49 marked as safe correctly = 50/(50+49) = ~50%.
100 people, 50 false alarms, 1 actual problem alerted and 49 marked as safe correctly = 50/(50+49) = ~50%.