If you really want to know, get your butt up on a ladder. i'm sure you know paint when you see it / touch it. If it's crusty like a caked-on salt (or something similar) and it rubs off when you touch it, then it's efflorescence. But I am confident it's not mold (it's not mould either!)
As for the grow-op suspicion; well it's possible, but what does it matter? If you suspect this house was abused, don't buy it. You can check around for other signs, like oversized electrical lines, water stains on the floor, unusual plumbing, or large bags of Doritos.