If mold is pushing cracking through paint, does it mean its inside the wall?
Really hard to say for sure; the only way to be certain is to do some slightly invasive investigating. Peel back the paint and see what is going on with the drywall underneath. Is it moldy? Wet? Water damaged? If you still can't tell, drill a 1/2&quot; hole and look at the swarf that gets pulled out by the drill bit. If you can get your hands on a borescope, try poking it in there. Then you'll know for sure.
There is one thing that is certain though: if there is mold behind the paint, it means the conditions under the paint are favorable to support its growth. Clean, sealed and dry sheetrock is not very mold-friendly.
Don't worry too much about saving the paint. At this point it's already failing, so it will come off soon enough even without help. Likewise, drilling shouldn't be a concern; if you're going to end up painting anyway, patching over a few small holes is no big deal.