'War Pigs' advancement can be triggered by opening a chest with corresponding loot tables, even though the chest isn't generated in bastions.

The bug

War Pigs, as the description describes, 'Loot a chest in a Bastion Remnant', should only trigger while opening a chest in Bastion Remnant. However, using command

setblock ~ ~ ~ chest{LootTable:"minecraft:chests/bastion_treasure"}

 and open the generated chest also grants the advancement, even though the chest wasn't generated upon world generation/structure generation in Bastion Remnant.