  We show that the discrete Kadomtsev-Petviashvili (KP) equation with sources
obtained recently by the "source generalization" method can be incorporated
into the squared eigenfunction symmetry extension procedure. Moreover, using
the known correspondence between Darboux-type transformations and additional
independent variables, we demonstrate that the equation with sources can be
derived from Hirota's discrete KP equations but in a space of higher dimension.
In this way we uncover the origin of the source terms as coming from
multidimensional consistency of the Hirota system itself.
