Q-NaLiqueur is defined by what is in it
The word liqueur sounds like a catch-all for sweet drinks, but Japanese tax law defines it by content: an alcoholic drink with sugar, fruit, herbs or similar added, with an extract content of 2 degrees or more. Extract content is what is left once you set aside the water and the alcohol. So the line is drawn by how much is dissolved in it, not by how sweet it tastes. Umeshu counts as a fruit liqueur, and that is why canned fruit drinks carry the same label. With the same ingredients but less extract, the drink falls into another class, with different tax and labelling.