It's not a misunderstanding guys, he simply lacks that bit of "common sense" or whatever you want to call it, that ordinary people have, due to the enviroment he grew in: if you read back to the quoted "chapter 10" you'll see this explained very well, by that other dude who was also inside that same enviroment long before the Kengan matches.
There's no room for a misunderstanding, he simply grew tired of shaking them off and decided to sort things out by killing them, he doesn't realize killing people is a bad thing because no one in his entire life ever taught him that, even the reasoning his grandpa gave him to cope with possible "moral issues" is enough to warp a child/teenager/young adult mind to that extend.
Ohma was the same in the previous manga, he changed when he met Niko and changed further when he entered "normal" Japan, Gaoh instead went directly from his previous enviroment into this new one, not enough time to grow or gets accustomed to this "new" society.