(From 11 May 2016 the Supplemental Classification is replaced by Image Type Tags:
see http://www.geograph.org.uk/article/Image-Type-Tags-update ).
The short answer is "Yes": Whilst in the past there was some degree of discretion if the camera position was close to a grid-line, current guidance (2016) is quite strict.
One of the aims of Geograph is to encourage people to visit all possible land squares. If there was not a general rule requiring the camera to be in the same grid square as the subject a photographer could go to the top of a mountain or tall building and use a telephoto lens to "bag" a number of grid-squares without having to visit them.