There is pi bond in both isomers, so if there is a pi bond repulsion, it must affect both isomers in the same fashion.
It is clear that the fact that the cis- exhibit higher mp/bp means that the cis- exhibits stronger intermolecular bonding.
The only way this can happen is due to that the cis-isomer must has an overall polarity, thus constituting for strong intermolecular bonding. Although the trans-isomer can pack better, both isomers essentially share the same number of intermolecular bonding sites. This means although the trans- has a greater density than the cis-isomer, it has a lower mp/bp than the cis-isomer.