There's two stages to be able to play FFXIV - When you register your FFXIV code, that makes your account active (able to buy service options etc)
But you are not allowed to play XIV until you buy an option.
Technically, everyone who has registered XIV to their service account has an active FFXIV account (since if they had an option/content ID/whatever) they'd be able to log in.
And having an active account = being able to apply for alpha
I hope this makes more sense to you, it's 7am and I've had no sleep ; ;