He obviously didn’t pay attention during the lecture on Newton’s third law.
That was my first “reaction” as well. But I don’t think the kick from a mortar firing would be enough to kill somebody. They make hand held mortars. I guess size matters. But it probably fell off of his head and then he got a mortar to the face/head.
Some 40-something guy in my suburb (where fireworks are banned) was with a bunch of people in a parking lot setting off fireworks. He got a mortar to the head (which he had set off) and died.