There are quite a few other forms of welding which don't use a welding torch to attach materials. Ultrasonic welding uses high frequency vibration to attach thin metal sheets or plastics. There is also roll welding in which two pieces are run by two high pressure pliers to clamp them together. Electricity may be used to weld alloys but software are a bit limited because the cost can be high.
We don't need to go through all the types, only know that welders have more than 1 way to create sparks fly.
Many kinds of metals out there may be welded to create a strong bond but there are exceptions to this rule. For example, steel and aluminum cannot be welded together because they have different melting points. As steel takes roughly twice the temperature of aluminum to weld, the aluminum becomes a liquid and will not stay near the steel.
But beyond this, when steel and aluminum fuse together they form a fragile bond that is not really effective.
The solution is both no and yes. Traditional welding is achieved by heating two pieces of metal that become molten along an edge and are fused together. Soldering involves not heating up the two pieces of metal but melting a lesser melting-point material between them to create a joint.
So, soldering is a sort of welding since welding involves heating and connecting two different elements but it is not just welding because it uses an intermediary to make a joint.