When it says "fixed one-time loot" it's referring to the chest, not the items in the chest. Meaning that chest (or whatever container) will contain those items only one time. If you reset the dungeon and open it again, you will find it empty.
If you go to the page of Toga of the Theurgist you will see other sources where you can find it: dropped by Hag in Abbey of Saint Admus. It is uncommon, not unique. Trust the wiki

But if you see something definitely inaccurate then please report it. For example if it says something is Unique but you find it multiple times, then you should report that.