In this analogy, it would be more like if "barrel" was a standardized unit of volume that everyone understood and used, but then in the oil industry specifically they used a slightly different volume and still just referred to it as a "barrel" because it's what they're used to.

And, whenever pressed for clarification, the oil people admitted "yes, technically our unit should be noted as 'oil barrels' which are different from the normal kind, but we like to just say 'barrels' because it's easier".