At least two thirds of the garage and all of the pool area are not beneath the house, they extend under what is presumably the rear grounds. I expect the pool location was chosen so that they wouldn't be heard by a housekeeper from the house.
From what I recall of the Toronto Life expose on the property, I thought the indoor pool and garage were under the house. The backyard has another swimming pool and hot tub for summer use. Think they had underground parking for 6 cars with a heated ramp and the indoor lap pool with a hot tub on the lower level. I could be wrong....but thats what I thought they reported.