If Shinjiro had the ability to tell what she was thinking, he would have said that he doubted Minato had been cowed into anything. When you've been beaten into silence, by other people or by your life's circumstances, you often lose the love and enthusiasm you had for the things you used to get excited about, learned to deny those things as you started to subdue the part of yourself that had gotten you hurt in the first place. Her brother wouldn't be doing the surprisingly outgoing things he did if silence had been forced upon him. At least, not as easily as he seemed to. Unless he had grown and rose above it, of course, but had Shinjiro been able to bet on it, that's not the conclusion he would have come to. Being forced into submission wasn't much of an Arisato trait anyway.

He does feel a bit guilty when she goes quiet like that. His life is full of plenty of things that he doesn't talk about. Aki's the same way. They rarely brought up Miki after she died. Never talked about the parents they couldn't remember. It just wasn't done. But when it was, you learned a few things. He can compare the memories to the blue-haired kid monopolizing the karaoke machine and come to a few conclusions.

"They probably thought it was your fault because you taught him everything." Her memories tell him that he's probably an intelligent guy. Quiet enough that he knew how to observe (though Shinjiro thinks he's already seen that). Absorb the information you saw and apply it on your own when it was to your benefit later. Get your little sister in trouble. Though maybe she had willingly followed along. Not like she had ever stopped being a goddamn pain.

Also hard to be painfully shy around someone who would put the textbook definition of outgoing to shame. Especially when you were a little kid, lacking adult inhibitions.