I disagree it is a false premise. If you look at major economies – other than the US and UK – >80%, >90% of units encountered in everyday life are metric. In the US, it is more like the other way around. The UK and the US are both outliers from the global average on this, but the UK to a lesser degree than the US is. No other major economy (for any reasonable definition of "major") is an outlier in that sense.
> We learn the metric system in school,
In the majority of countries worldwide, people only learn the metric system at school. The US is an exception in having an education system which still teaches non-metric measurements.
> Sure, Americans also use non-metric units, but that's not as unique as is claimed. First hit for "site:.uk mpg" is "MPG stands for miles per gallon and is used to show how far your car can travel for every gallon (or 4.55 litres) of fuel it uses".
That's not a very good argument – the US and the UK are the only major economies to use miles for road distances (and hence also speed, fuel efficiency, etc). All other major economies use kilometres, not miles.