Wait hold on. Even if they were different windows that doesn't mean that Yujiro shouldn't be able to slap jack out of it? Is Yujiro getting weaker?
When he said "different windows", he doesn't mean "you replaced the windows I broke", he means "these windows are made of a different material than last time".
It's pretty clear that the windows were like 6 inches thick of plexiglass. Which is bulletproof glass. Which doesn't just "shatter" and normally isn't built more than half an inch thick anyway.
Yujiro could've pushed Jack forcibly through if he knew that's what they were and that was still his goal--the fact that his head made it all the way through is proof. But he clearly only kicked or threw Jack into the window in the first place, so when Jack's head smashed into the window first, the force would've been transferred into the window slowly as his head broke through, and by the time it got to his neck it clearly had absorbed enough force to not break further.
The author understands physics lol. I know that must be shocking, given
gestures to the entire rest of the series