They are responsible, for two reasons. One, they caused the damage so they have to repair it (including repainting). Two, the ceiling is common property and they have duty to maintain and repair CP.
They might say, well, this has happened to everyone so if everyone just fixes their own ceiling, it will all even out. Don't fall for it. Any half decent strata manager or building manager will find a contractor who will charge less per ceiling for doing a whole block than it will cost to individuals.
And make sure it's repainted too – that's another favourite “not our responsibility” bluff.