In general, all the electricity consumed by an electrical device gets converted into heat. If your GPU uses 250W of power, it generates 250W of heat. If your whole computer draws 1kW from the wall, it generates 1kW of heat. If your little raspberry pi and its power supply together draws 15W from the wall, it generates 5W of heat. A 1500W electrical space heater converts 1500W of electricity into 1500W of heat.

So yeah, you're not wrong.