This is true. You can find the 'American style' in the UK occasionally, especially in fiction – it's not exceptionally rare.
But regardless, the styles have come to be known as 'American' and 'British' because they generally are preferred in American and British English respectively, even if it's not absolute: Americans tend to be taught US style, and Brits tend to be taught British style.
But regardless, the styles have come to be known as 'American' and 'British' because they generally are preferred in American and British English respectively, even if it's not absolute: Americans tend to be taught US style, and Brits tend to be taught British style.