There’s a good chance that Moss will declare for the draft, but I don’t think that’s what he’s saying in that post. On Twitter he said he’s planning to come back stronger than ever.
Moral of the story? Don’t read too much into every tweet/post that kids make. I suspect he will declare so he can get his draft evaluation, and then make a final decision based on that feedback. Between now and then there will be lots of theories, voices, and interpretations on what he’ll do.