Bearing walls are sometimes poured with the foundation, it is not unreasonable for a interior wall in a basement or some commercial structures to be concrete.
teddybound
I’m still far from convinced it’s a concrete wall, although that’s not unknown. I would still obtain an inexpensive screwdriver and poke around in the bottom of the hole. Concrete and wood are very different and you should be in no doubt as to which you are dealing with in short order. The repairs aren’t much different, although I’d consider Durabond over drywall compound if it’s a concrete wall.
zuer-coli