I would call it a latice of thin sheet metal hooked to wires suspended from the ceiling that hold the sheet rock up
Sounds like metal channel hung from the old ceiling or structure with the sheetrock screwed to it. It's the usual way to construct a dropped commercial sheetrock ceiling. There is always limited access (if any) to the space above via access panels. Can't have them every few feet.
I certainly wouldn't call this "frail" just because you are not familiar with it. It's on par with any ceiling grid system. No, it can't be walked on unless you want to fall through.
I would suggest that you try to learn something about construction if you are going to be running cables in buildings.
-Hal
