How does that square with his Wikipedia page:
While a senior at Marjory Stoneman Douglas High School in Parkland, Florida, Hogg was on campus when the shooter, Nikolas Cruz, a 19-year-old former student at the high school, started shooting with a semi-automatic rifle after pulling the fire alarm. Hogg, who was in his AP environmental science class, told the teacher around 2:30 p.m. that the repeated “pop” sounds the class heard sounded like gunshots.[4] Hogg and other students made an attempt to exit the building, but a janitor instructed the students to go back into the class. A culinary arts teacher pulled Hogg and others inside her classroom and they hid in a closet.[4]
Note that ref 4 is http://time.com/5161034/florida-school-shooting-survivor/