I can't really fault a human for having emotions, but kenta's facial expressions don't really match the vibe he had earlier in the story
the one introduced to us before was like a sleepy look and man of few words, this flashback arc he is very energetic and expressive eyes, even though it's technically the past and the future one had that quiet vibe too, almost seems like a different character entirely
although when i look back the art style has changed a lot too, natural to happen over 8 years, so that's probably part of it