What the article means is that the suspect thought the gun was firing blanks (it was) so he assumed that it wouldn't be deadly, even though blanks are discouraged around other people.
part of the wadding or seal came out and injured the victim, which rarely happens. In court he evaded charges for carrying a loaded firearm (I guess blanks don't count as loaded) and obviously there was no intent to harm, only to make a loud bang or something like that. Either way he was charged with injuring the victim and probably got sued as well