In terms of the Rav Shach story, the way I heard it was that they came to him with a question about the Ramban, which is not an appropriate thing to come to a Gadol Hador about – you can ask your teacher, not Rav Shach!
He then served them some cake, asked them if they liked it, and asked them if they know how to make it.
If you tell over the story a certain way, it can sound like he was being very charif, and as JF2 pointed out, that is not usually the best way to deal with people.
However, it is possible to tell over the story in such a way that you stress the fact that he spoke in an adin fashion, and he was just trying to remind them that as important as it is to learn Ramban, it is also important to know how to make cake, and even though right now they are in school and being made to feel like their only purpose in life is to learn Ramban, they have to remember, that one day, there will be more important things for them to know.
When girls are in school, they are made to feel like the only thing that matters is knowing Ramban, so perhaps he wanted to give them some perspective.