It's a young field and one consequence is it's still lacking clear direction and an established body of knowledge. using the term "smart" does of course smell a bit, but there's a reason for it.
The main impetus behind being "green" at this level isn't so much save the planet as it is "we're heading for a time where energy and its distribution genuinely becomes a problem". So, the objective is energy efficiency for the sake of stability of supply.
One point most people agree on at this point is that a key is going to be employment of technology to reduce our exposure to energy supply fluctuation. In many cases, this is information technology (e.g. smarter algorithms for HVAC) and in other cases it's going to be changing the technology in the field (smarter energy meters in homes, that can report back and come with a web UI so the homeowner can assume greater responsibility for how they are using energy) and in some cases, it is fundamental rethinks of how energy is distributed (e.g. more decentralised energy grids, harmonisation of energy transfer protocols and technology across national buondaries, and accounting for the emerging option of individual contribution of surplus energy back into the grid).
So there's a lot of Lego blocks most of which are quite sensible and no one's quite sure how they all fit together just yet. So when we're talking about how all of that works together, we tend to use the term "smart city" to denote an overarching context. This context is necessary because it helps keep the big picture in mind. A practical example is, the energy meter manufacturers' association as they standardise what protocols a smart energy meter employs, they need to include the people working on smarter intelligent HVAC. The public transit people might be working on concepts for unattended light rail systems which the traffic planners need to be aware of.
I'm not saying that the expression "smart city" is not unnecessarily vague, but it's useful to the people working on reducing vulnerability to energy crises because it helps them remember that it's a larger complex canvas than the little square inches they're individually working on.