Bathroom flooded by condo upstairs. Can there be mold on the drywall between the floors?
If it was a toilet ring, you can be sure that it gradually started leaking longer than two weeks beforehand. It takes sometimes weeks before a slow leak accumulates enough water and softens the gypsum board enough to leak down to the ceiling below. There may very well be mould above in the ceiling space. This should be investigated asap and the appropriate authorities contacted (insurance company, condo committee, etc.) so that you are not ultimately left with the mitigation costs when it is clearly the neighbour's fault. Mould can be a health hazard. You want to be sure that there is none in the ceiling space. Good luck..