They often have pretty powerful heaters for defrosting, even your household fridge has a heating coil tucked inside somewhere: Ice takes a lot of energy to melt quickly, and refrigerators are very well insulated so once they're heating up there's nowhere else for the heat to go. Refrigeration (using phase change) is paradoxically much more energy efficient than electric resistance heat (which is what is usually used for defrosters, because of cost minimization) so it's not uncommon for the defrost heater to be significantly more powerful than the whole refrigeration side, because the defrost heater is only intended for very occasional use to literally de-frost the coils before turning off again. In this case, it sounds like the de-frost heater was used repeatedly or indefinitely and the cooling shut off.