Well. This is Nicholas going from irritated and worried to a little wide-eyed, and his cheeks darkening a little. Despite every indication, apparently getting outright approval from an adult still has an effect on him.

"... thanks."

... and then the flinch gets him right back into concerned. Very concerned.

"All right. There was a fight. Is that why the whole city is empty?" It might be, but he knows the people... one fight, however terrifying, would have sent them hiding, not... packing.