Like farmerboy said, training doesn't necessarily cure carelessness or stupidity.
The guy's been through mandatory training. According to the news, he has a carry permit, which requires training.
Furthermore, he's a security officer. He's pictured on facebook in two different security uniforms (with what appears to be his Ruger 9mm), and lists his employers as the county school district and a local pharmaceutical company. Armed security by FL law requires a G license, which requires 28 hours of training- above the 40 hours of D license (unarmed) security training. And yearly qualifications.
Most employers here require law enforcement or military experience for armed security. He has a picture of a Virginia Tech campus police badge posted, too. So he may have had law enforcement training as well.
http://www.facebook.com/people/Moise...00002908288043