Is that the only person you've ever heard say that? It's possible where you live differs from literally everywhere else, but more likely he was wrong or lying. In the entire rest of the country hard means crack and molly means MDMA (or more likely, it's MDA or meth than actually MDMA, but that's called "a scam" not "I guess meth is molly now.")
Formaldehyde and PCP are both referred to as "wet" (with PCP being far more common), but hard is always crack (or sometimes soap/drywall, also scams), soft is always coke (because it's mushy if it's good rather than actual powdery powder), molly is always MDMA or one of the aforementioned scams, and girl, boy, white, dog food, all refer to their specific drugs respectively as well.
Speed also shares two, adderall/dex ADHD class drugs (older) or full blown meth (newer).