Derrin listens, processing as best he can, as it goes. It seems like mostly confirmation. "It is not meaningful to say of Earth that it as a whole has made any choices" seems more scathing to him than anything Thellim has yet said. Presumably they have, in a sense, made the choice not to set their whole planet's land areas ablaze; but a charitable interpretation of Isabella's statement would be that this is only because people have individually not wanted to set those fires, not because coordinated Earth made a decision apart from those individual choices which could effectuate those individual choices.
Then one point jumps out at him. "You are yourself a precognitive psion?" In retrospect Derrin should have prioritized asking about this point much earlier, but he is smart, not wide; he is juggling a very large number of balls. "Is this conversation, itself, one that you have selected from among many possibilities?"