Yes he was....he was huddled in a closet with other students.
He went home a while later and grabbed his camera...and that's where that story appears to have come from.
He was not in the building where shooting took place. He was "on the campus." Hogg has used confusion created by his own badly articulated account to suggest that stories claiming he was "not at the school" are fake news. But Hogg has (deliberately, IMHO) conflated the (false) stories that he was not on campus with the (true) stories that he was not actually in the building to suggest that his life was in imminent danger.
He was never at any time during the shooting in the same building as the shooter. That is a fact.