My thought would be that "Stopped" means the armed citizen killed or incapacitated the bad guy, ending the shooting, and "Saved Lives" means a situation where the armed citizen failed to end the shooting but prevented additional loss of life, such as covering people escaping, suppressing the shooter for a time until backup arrived, etc. Every time the shooter was stopped, lives were saved, but the reverse is not necessarily true. Lives could be saved without actually stopping the shooter.