I collected all three stars of horai in the event that just ended early this morning. Before the event ended, the description of the items read something close to "collect three stars to empower the horai dragon!" Once the event ended, the description was changed to "collect three stars to empower the horai dragon in the carnival 2020 event!" which seems to imply, just as my lack of reward seems to imply, that it was exclusively for the horai dragon from the event, which was not indicated even in the slightest before the event ended. I feel thoroughly duped, and I want my orbs.
Edet: This is not a bug.