Not true at all. I went from "no computer science background" to a Django junior hire in ~10 weeks of (admittedly quite intense) self-study. I'm now employed as a mid-level programmer making very good money.
My anecdote is about as valid a characterization of whether it's possible in general as your sweeping, baseless generalization.
It's very subjective to talk about what a "rails junior" means, but it is very possible for someone (like the students at Code Academy) to learn an immense amount of programming knowledge in a short amount of time (say 12 weeks).