The relative, coplanar angular distributions of electrons, produced in an electron-impact double ionization of helium (e,3e reaction), have been measured at 1.1 keV impact energy. The momentum transfer was 0.45 au and the two `ejected' electrons were detected with the same energy of 10 eV. The general features of the angular distributions are discussed. The data are analysed in different angular modes which allows a detailed comparison with state-of-the-art calculations. For high incident energy and small momentum transfer, as in the present case, the (e,3e) cross section can be related to the single-photon double ionization (PDI). We exploit this fact and compare the present findings with the PDI and identify the contribution of non-dipole effects.