Because he was not roleplaying Vael, he was roleplaying Daxton, who is an equal member of the Nomads.
As you approached him and shot him he told you to either bring Carlito, so your boss would explain that you and Nomads are allied or to just end it all, as you had already shot him and breaching the alliance with the Nomads, that's when you should've stopped, but you decided to murder Daxton by which you breached our alliance and gave us reason to name you Heathens.
As if that wasn't enough you went and scammed Arty, who is a high ranked member of the Nomads a few hours after killing Daxton. So you not only murdered our men but scammed them.
Than as if that wasn't enough you went and lied to Carlito that you did not kill anyone. Who lies to their boss?
Anyway, enough of that. You boys have fun now, I have a chapter to write.