Elastimaric is the type of paint. It’s a rubberized paint.
But. There actually may not be that much water there. It may have eroded away at the thin layer of paint in such small amounts that it just looks like that.
Years ago , I had that happen in my apartment after a tornado took shingles off my roof. The water bubble was only about a quarter of that one. You could fill a swimming pool with the one in this photo
In more concerned that they'd rather take a picture then move all their stuff first so it wouldn't get wet if it happened to burst right then and there.
Probably so that when they tell management that there was a leak in the ceiling and it flooded their room, management believes them. I’ve worked for a property manager that charged a resident for a busted door that happened because there was a break in and she almost died - and my boss didn’t believe her. If I had that kind of property manager I’d be taking pictures too