As much as it may be uncomfortable to say, it sounds like they may have been justified in killling the invaders who were there to take land and kill their people. “It’s complicated” seems to mean, the white people there probably deserved to die, but it’s not comfortable to say so.
The apology is warranted.
ETA: “deserved to die might be too harsh... understandably the target of the Tsilhqot’in defending their land and people might have been a better way to put it.