It sounds like your Dad had a flaming pellet. If he was shooting pellets, what happened is for some reason one did not burn through and so what you saw was a flaming pellet come out the end of the barrel. If he was swabbing with Shockey Gold, he might have not dried the barrel well enough. It's hard to say without being there..

Do you have to swab after each shot? For the best accuracy, that is normally the way to do it. Although I will often times shoot twice and then swab, it depends on the bullet.