British imperial units and US customary units were actually both codified after American independence! Both British imperial and US customary units are derived from earlier English customary units. We made some agreements to harmonise our two systems over time so that we were at least using the same pound and yard, because we weren’t before, but somehow volume units escaped this

Ironically we did sort of hamper your early efforts at metrication completely unintentionally; British pirates (privateers, more accurately) captured the French ship that happened to be carrying standards for the metric system across the Atlantic to you

Either way, Brits definitely shouldn’t make fun of anyone for their system of measurement, because the only thing worse than a non-metric system is using some cursed half-and-half Frankenstein mashup of both metric and non-metric