Toilet and Ceiling..

I woke up the other day and as I made my way to the bathroom I heard noises. Water was pouring through the drop ceiling panels above and dripping everywhere. I ran upstairs to tell the neighbor (who I don't know) and he didn't hear the knocking on his door. I did an online check to get his phone number, called him and he said his toilet was running all night and he just stopped it a few minutes ago. I don't know why but I didn't believe him. I have been in homes where rain has made its way through a roof down to the ceiling and I have also experienced the back toilet tank (clean water) leaking from an above toilet and although the water is dirty and the smell is bad until the ceiling dries, I have never known the water to be this particular color of dark brown to dark red with a stench that choked me it was so bad. But anyway, my question is should I be concerned with mold?

As man who does odd jobs for the land lord and lives in the building, said he fixed the toilet upstairs then wanted to hurry up and come in to replace the 1960's drop ceiling panels that were wet.

I found that to pre premature on the side of the Land Lord. Especially since whatever is up under the drop ceiling is soaked. What can I do to confirm whether or not it was the toilet tank and not the toilet bowl that overflowed? What should I do regarding the ceiling?