I don't know, Nate apologizing doesn't seem like that huge of a change to me.
Well, apologizing to someone who tried to kill you, as opposed to killing them, seems like kinda a big deal. I'm not gonna debate about if he was right to kill them or not, though, that's a different subject.
Nate would have apologised in a low tone which suggests he was annoyed meaning he didn't want to apologise but he did probably because of Russ. As Harp said, it would have probably shown him respecting Russ a little more or a little less.