not a teacher
This is probably referring to what is often called a "hung window".
Here's an illustration.
As you can see, the bottom half of the window is opened by lifting it upwards. In a "single hung window" only one half of the window will open, in a "double hung window", both the top and bottom halves can be opened.
By saying the window "shot up", the writer means that it opened very rapidly, suddenly.
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