Those kids probably have never played D-game properly.
The panda teacher used to invite people to murder them, no?
So he probably invited the senpai to do that. But since Kaname defeated the panda, the senpai probably never went into an actual D-Game Fight.
He only received powers and assumed that the app was just there to give powers and money.
Kaname only assumes that the guy is B-rank because he has a "clan".
But a group of kids can still call themselves a "clan", even if it isn't an official one.
So our MC is currently bullying/traumatising a group of innocent children (well, they are delinquents, but they're still innocent compared to the standard D-Game Player).
And I'm ok with that.