As Pip says this is a suspended beam and block floor drawing. But the picture you showed me looks like a solid concrete floor.
Pip points out that builders can and sometimes do their own thing, and the building inspector can allow variations to the design during the build and as the garage is not a habitable room it is possible the builder was allowed to do a solid floor.
Can you make a hole in the floor and investigate at another position to the cable access points.
The drawing shows 75mm of reinforced screed, you should be able to identify that and then see beams on or dence concrete blocks or a solid concrete floor.
There should also be air vents every 1500mm around the DPC level if the garage was build as per drawings. And if you make a hole in the floor your drill should punch through into an open void.