It was apparently a training situation using live fire, so many people could have been present, and in close quarters.
The devastation still seems high for such a light round.
If you watch the HBO movie “Pacific” one of the people it follows is Eugene Sledge who fought throughout WWII as a 60mm mortar man. Plenty of scenes with his crew in action.....
Sledge wrote “With the Old Breed at Peleliu and Okinawa.”
Mortars are very effective weapons in combat. The little 60mm comes with a killing radius, that is killing not wounded, of 10 to 15 meters. If you are vertical, and one of those puppies goes off 30 to 45 ft away you can be in serious trouble. Made excellent boobie traps in Viet Nam.