A lot of apartments are just converted houses, or old with minimal such standards except basic structural. So the floor joists would typically be 2x10 (nominal inch). Possibly a neighbor below tried to install the pole and found only drywall ceiling and cut a hole. Instead of boxing between the joists and attaching to that, they just went higher to the next flat wood - the subfloor ply under the flooring - so possibly just 3/4".