Not a design expert, but maybe this is also to mitigate against icicle formation? I am an expert in defending against personal injury lawsuits, and a giant icicle falling off a building could easily cause one...Yes those are heating cables, they will be covered with pinned insulation against the concrete. The soffit will be a cold space, cables turn on via thermostat. Not necessarily a "heated floor" above, but there to make sure you dont feel the cold during winter. Here the concrete is what 5-6 feet thick? Cant see much heat or cold migrating up, will keep slab warm tho.