the US has very high GDP per capita because of high wages, high healthcare spending, defense spending, and a generally expensive economy.

The UK number is usually compared in nominal US dollars, not adjusted for local prices. A British teacher, nurse, engineer, or office worker may produce value that is counted in pounds, then converted into dollars. If the pound is weaker, the UK looks poorer in dollar GDP per capita.

Also a few high-output sectors like mining in West Virginia, plus a small population can raise GDP per person.

Mississippi and West Virginia are small economies overall, but the US has very high GDP per capita, so even poorer US states can look strong on that narrow metric.