About Tigur's tribe... they're like aggro creatures in game who attack anyone approaching their territory. So, they had it coming.
Serena's narration is supposed to be longer... well, the core idea is the same.
My favourite is when she asks Tigur, does the people captured him, or the slave traders, ever say "killing is bad".
Of course they don't, because those soldiers kill people, and they put their life in the line.
Also... clarifying page 11... what she meant is, when the people they said it to (such as the children in slum) is in danger, the people saying "killing is bad" won't be there to help.
...the LN doesn't mention about Rick wanting to put Tigur to work. He just say Serena picked the boy, so he's hers to take care of.