You should be able to appreciate that different people have had different experiences, and in a place as large as the US, there are going to be a whole slew of them.

I personally studied metric in elementary school and middle school. It's what's used for science, how could I not have? If others didn't learn that and instead had everything in imperial, that's news to me. It's perfectly possible though, with just how large the US is. It does make me a bit surprised that Missouri of all states taught this, but maybe it was unique to the district.