Kansho wrote:It's a possibility, that's all. Maybe as she had more time with Shirou (he accompanied her at home, they talked in the classroom) and Rin appeared as a conversation subject, some feelings were triggered into Sakura and Zouken saw them.
Or simply here Zouken was smarter. Probably the dialogue happened in all the routes, but he wasn't able to crack her determination.
It just hit me when I read your post. The triggers.
The question about Rin did appear while walking Sakura home. Sakura was moved by that a bit, because she knew he liked her. The feelings of resignation surfaced a bit.
When she saw that Reiju appeared on Shirou's hand, it was a shock. She was feeling down for the whole day. Again, the feelings of resignation.
At that point all the routes can still be chosen.
The last trigger is when worried Shirou comes to check on Sakura.
Sakura always thought that Shirou should be with someone else, but when he came worried about her, she once again wished to be with him. At that point she realized that it's not an impossible wish.
Shirou once again changed her words from "give up" to "keep going".
Zouken's line would be the same in all routes if he's the same old bastard. He knows what kind of feelings Sakura has for Rin.
But due to all the triggers, Sakura would have these thoughts in Heaven's Feel:
Rin is participating in the War
Rin will win the War
Shirou got involved in the War
Shirou cared for her
She could be with Shirou
But Shirou will be killed by Rin
I think that would be a pretty good explanation.