Bug. Offering the reward in the casino unlocks the opportunity to sacrifice and buy offering upgrades even without a built offering pedestal.
Looks like you still have to build it before you can benefit from the offerings though, so probably not a huge issue.
You can always buy and sacrifice, but offerings don't add to storage until you've built the pedestal, and you can't sacrifice/upgrade a resource until you've bought the corresponding offering pedestal at least once.
