I'm not sure either, but I guess the key term was "distinctive" in the United States federal guidelines, which might be where the misconception came from. Also, according to this article, in 2020 in the United States federal regulation, flavor was dropped:

Until recently, vodka’s long-standing federal definition was “neutral spirits distilled or treated after distillation with charcoal or other materials so as to be without distinctive character, aroma, taste or color.”

and then they go on to regarding the new standard:

we have a new standard of identity: “‘Vodka’ is neutral spirits which may be treated with up to two grams per liter of sugar and up to one gram per liter of citric acid.” While neutrality remains part of the definition, for the first time since 1949, the standard no longer defines vodka by the character it does not possess.