To his credit (or perhaps against it), Minato fails to look particularly sheepish on being called out. Instead he shrugs and shifts his gaze to the road ahead.

"Sorry. ... it's nothing."

He doesn't feel it's productive to tell the truth here. He doesn't want to say, 'I was just thinking about the last time I saw you and wondering if this is what Akihiko-senpai and Mitsuru-senpai felt like seeing either of us up and walking. And I was wondering how different and how the same things were between my sister's world and mine. If you were more or less at peace there. And if you were going to be okay here.' Because he doesn't want to darken the mood or pry. And besides it isn't like these thoughts particularly matter outside of his own introspection and adjusting to the differences of this place.