Yeah i suppose they are Facebook like-gating that Button but this is against Facebook TOS since November 5th, 2014, so i smell trouble coming...

Facebook has changed their policy on incentivizing people to like your page. In the past, you were allowed to require that people must Like your page in order to receive some incentive such as entering a promotion, obtaining a coupon, or viewing content. Beginning November 5th, 2014 Facebook policy now prohibits incentivizing for people Liking you page.

The bit of their API that allowed third party app developers to create like gates was removed. App sellers like Shortstack were forced to adjust. The final removal of the like gate was performed on November 5, 2014. The functionality itself has been removed, and if you’re found trying to replicate it through a third party app, that app is liable to be removed as well.

So if this is no Bug and they hide the Button to get the Key behind a Like-Gate, they probably will be disciplined if not removed immediately!