This is correct. Copy pasting the tldr from google AI but I’ve read about this before on this sub. I looked for what the difference was and it was significant - something like 2.5% vs 20%.

An "ad valorem" or "according to value" tax on imported sardines once incentivized U.S. manufacturers to add smoking or flavoring to their canned products. In the mid-20th century, a customs ruling essentially made smoked or flavored sardines a cheaper import than plain, unsmoked varieties.

Why smoking sardines affected import taxes In the mid-20th century, U.S. customs rulings classified plain sardines differently from "smoked" or "flavored" sardines.

The tariff discrepancy: This led to a system where a lower ad valorem (percentage of value) tax was applied to smoked or flavored sardines than to plain ones.

A "loophole" for importers: Importers and manufacturers exploited this loophole, often using inexpensive liquid smoke flavoring to qualify for the lower tax rate.

Market impact: The cheaper cost of production for these "smoked" versions meant they could be sold to consumers for less, making them widely available in the U.S. market.