Suppose there are two atoms, A and B.
Firstly, if the two are bonded together.
the nature of a covalent bond is the attraction force between the shared electron pair and two nuclei, positive and negative, electrostatic force. The attraction force between A and bonded pair, attraction between B and attracted pair. So two forces.
However between non bonded two atoms, I don't quite understand either because I think this should be the case when van der Waals force comes in. I guess the statement in your revision guide could mean that, the attraction between the nucleus of A and the electrons of B, attraction between the nucleus of A and the electrons in A, and so forth. Therefore, there are four attractive forces, possibly. But personally, I think this will just perplex students a little bit, well, a large bit, as the case of two non bonded atoms resembles that inside noble gas. Eg, Two He atoms.
Hope that will help.