Cold weather will mess u0 leather, because it changes how the leather acts, in this case I would say it caused it to stretch instead of simply flex, which caused the tumbled effect to be kind of ironed out.. Returning them won't change anything as it will simply happen to the next pair if worn in extreme cold.
I wouldn't worry about it to much, like similar effects are bound to happen under wear over time anyways. Now I would be concerned if the tumbled leather throughout the rest of the show lost its texture, that to me would be return worthy.. But he tongue is a high stress area