The figure you’ve linked plots concentration by weight (wt.%), while the alcohol content of drinks is usually given in volume percent (v/v). Ethanol is less dense than water, so a 30% concentration by weight is a higher concentration by volume.

Imagine a 100g solution of 30wt.% alcohol. That means that 30g are ethanol and 70% are water. the 70g of water translate to 70ml volume (density 1g/ml) and the 30g of ethanol translate to 30/0.789 = 38.02ml. So in total, you would have 108.02ml of liquid and the concentration of ethanol by volume would be 38.02/108.02 = 35.2%.

Why it gets wacky at the end: Ethanol freezes at -114°C, water freezes at 0°C, but at specific concentrations, the eutectic composition, the solution freezes at a lower point than either of its constituents. The eutectic point is the lowest possible freezing point of a solution. The formula I gave is not applicable to eutectic solutions and is an approximation based on perfect solutions (which in reality don’t really exist).