Potentially not a bug, but it is possible to obtain the Ice Bucket Challenge advancement when getting obsidian from a piglin trade.
Linked issues
Comments 5
It's now WAI - this was "fixed" by changing the description to make this make sense. "Form and mine a block of obsidian" -> "Obtain a block of obsidian"
The advancement uses the "inventory_changed" trigger and merely checks if the players has obsidian in their inventory. It was also obtainable through obsidian found in loot chests. Either the description should be changed or the trigger should be changed.