I've no idea of your location, nor any idea of the construction of said apartment.
Around here, you're not allowed to 'drill into the floors' of apartments. Most apartments here are made with 'pre-stressed' concrete floors. That means (as has been explained to me specifically for this purpose) that there are cables running the length of the floor. And they are tensioned. Story has it, that one person drilled into the floor on a location, specifically to bolt-down a safe. He hit/weakened said cable, cable snapped, and the floor broke/collapsed etc. and he was liable for it.
How much truth there is to ANY/ALL of that story, I can't say. Nor do I profess to knowing details. This was well over 25 years ago, too.
Just another arrow in the quiver of knowledge. Could very-well be a practice/training arrow, too.