There are many other forms of welding which do not use a welding torch to connect materials. Ultrasonic welding uses high frequency vibration to connect thin metal sheets. There is also roll welding where two pieces are run through two high pressure rollers to clamp them together. Electricity can be used to weld metals but applications are a bit limited because the cost can be high.
We don't have to go through all of the types, just know that welders have more than one way to make sparks fly.
Many types of metals out there can be welded to create a strong bond but there are exceptions to this rule. For example, aluminum and steel 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 aluminum and steel fuse together they form a brittle bond that is not very effective.
The answer is both yes and no. Traditional welding is done by heating up 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 lower melting-point material between them to cause a joint. So, soldering is a form of welding as welding involves heat and connecting two different components but it is not strictly welding as it uses an intermediary to create a joint.
Welding is a serious profession with no small amount of danger involved. However, everyone needs to be able to laugh at themselves no matter how dangerous their job. Here are a couple of good humor ways to assess if you are talking to a welder.