To me it reads more like a methd to keep players who are getting SB around launch to have a little incentive to buy a bigger sub card despite beating the MSQ.
Basically, it's a reward for sub retention for early Stormblood players.
Honestly, if they could just say "Have a copy of Stormblood registered to your account during the campaign," instead of "Purchase and register Stormblood during the campaing," there would be no confusion or worry.
