This was the second time I got this (I presume) bug where I completed the same daily quest twice.
From what I've seen this only happens in a very specific case.
When you log in the first time in a new day and you instantly clear a quest by doing an activity that was rolled into a quest you get when they are rolled, it seems to not get flagged as "already being there" on the checklist when rerolling other quests. So after you completed that quest you can roll the same quest again and complete it again.
In this example I completed the Papaya quest on login and got it again when rerolling daily quests.