Yep, I see that too. I don't ever remember seeing that in the past.
What it looks like to me is the option to add extended services/bonuses to your account. Onion Helm, Goggles, or even register future expansion packs for XIV. What Beta Test is doing in that drop down box I have no idea.
Unless SE has changed the way they do things, there is no Beta Key. They simply take your account name, and activate Beta onto that.
Although... last time ZAM did a Beta Giveaway, you had to fill out a form with the E-mail address your Square Enix account was attached to. It doesn't look like that's the case this time? Maybe they really have switched over to Beta Keys.