You were basically freeloading on your neighbors; there is no way you'd keep 20C inside without any heating source. Without your neighbors footing the bill you'd have ended up with massive hard-to-get-rid-of mold patches near windows by spring.
If he shut off his heat counting on neighbor heat to keep him warm, then maybe it would be freeloading.
But if his heating system was on and he set the thermostat to 20℃, which is in the normal indoor temperature range according to most sources I've seen, and it just happened to never turn on because his neighbors set theirs to higher I wouldn't consider that to be freeloading.
https://www.energy.gov/eere/buildings/zero-energy-ready-home...