I take your point about things being plain wrong as far as the Window Tax is concerned.
However, I have memories of buildings with bricked up windows, and probably in buildings that were from the post 1851 period, so what would be the explanation ?
I am not a historian, neither in a general sense, and especially not as far as local taxation is concerned. Is it just possible that, some time after the Window Tax was abolished, one of the components of the calculation of Rates was the number of windows in a building ?
If so, the teacher concerned would be guilty of identifying the wrong tax, but not guilty of identifying the primary reason for the bricking up of windows.
It is much easier to tell kids to look up the Window Tax on wiki, than to suggest that they research the manner in which Rates were calculated. As you say, identifying the right reason but the wrong answer, may not be viewed too severely in today's education system.
Phil.