Richard Jewell really was sick the day it all happened according to “The Ballad of Richard Jewell” an article published in Vanity Fair that formed the basis for the film.
The bag also shifted at some point, causing most of the explosion to disperse into the air rather than the crowd.
Jewell did find the bag holding the bomb after dealing with a collection of disorderly drunks—though they were reportedly adults, not kids as shown in the film— and it was when it was discovered the bag didn’t belong to any of them that Richard realized there was a problem.