A fridge moves a certain amount of heat energy from the inside to the outside, but that doesn't come for free. You have to put extra energy into the system to make that happen. The hot side of the fridge gets the "moved" heat plus the heat from the work you had to do to move the heat. The work heat is waste.
If what you're trying to do is make something hot, you're moving heat energy from the outside to where you want it to be hot. That makes it hotter, but it requires work. In this case, since you want to make things hot anyway, that work heat is extra bonus heat.
Say you have a 1kWh budget of energy to spend to heat a room and access to a variety of heating methods such as an air pump and an electric resistor (space heater or computer). Which one should you choose to maximize increase in warmth? While the electric resistor will convert the energy it uses to heat with a very high efficiency, the air pump will usually heat the room even more because it doesn’t just locally convert electricity to heat, it moves heat from outside the room to inside the room. Further info in [1] and [2].
EDIT: great explanation/details in sibling comment by ’prutschman’.
Think of the way your fridge works, but your house is the outside of the fridge and the ground is the inside of the fridge. That is, the heat pump uses electrical energy to move heat from the ground (more specifically a deep hole that is drilled) into your house. It takes less than 1J of electric energy to move 1J of heat, therefore one can claim an efficiency >100%.
