If it is only "American blueberries" that can be called blueberries, it would be a very poor choice to carry that drink as a signature drink for a Finnish company, wouldn't it?

And I'd say they have been called blueberries in local language for thousands of years. It is just when you do a word-by-word translation to English you'll get an overlap with the English name given to the berry in NA (once the Europeans "discovered" America, that is)