This kinda confirms a suspicion I had a while ago that Tsuyoshi is pretty much like... I wouldn't say inhuman or anything like that, but he's definitely different in a way. Like, the way he looks at people, his eyes, his expressions... It's very different from everyone else's in a way. But I couldn't put my finger on it for a long time. I'm pretty fond of sinister/blank/empty-eyed expressions in manga so he stood out that way for me in this one... and I thought it was just an aesthetic quirk.
I'm glad the mangaka is going this route, at least if they are going where I think that they're going...
Putting that aside, Tsuyoshi's mom is obviously very weird. Maybe she does love him, maybe not. I'm not exactly sure. But she's definitely obsessed with 'normal'. Maybe that's why Tsuyoshi just wants a 'normal' life. It's been drilled into him for a long time. I feel like the smile has some sort of significance... Maybe not mind control like Doomcard said, but definitely something. A pattern that Tsuyoshi knows all too well. I hope we can find out soon.