When using the "/loot insert" command, even when only one type of item is included in the loot table, if you insert the loot into a pot, you get the error message "Target position Pos(-18,1,-45) is not a container", even though it is a container. I tested this on a furnace, which also only has one inventory slot, and it works just fine. In conclusion, for some reason, pots are not considered containers when using the "/loot insert" command.