What makes a type of energy low or high grade is its ability to transform completely to another form. Electricity can be transformed 100% into thermal energy, thermal energy can't be transformed 100% into anything.
You got the general idea correctly. If the question read "high grade energy for a low grade task" then technically electricity is used to heat something (high to low grade), but I still think the ground source pump isn't the MAIN source of energy for heating. The main source is the thermal energy in the ground and the pump is used to circulate the fluid carrying that energy to the colder space. To put it another way, the amount of thermal energy required to heat the space is much larger than the work done by the pump alone, thus it's not the main source of energy and shouldn't be considered an example of high grade energy used for a low grade energy task.