Some peoples fingers may naturally swell in winter when you're out in cold weather and have your fingers exposed to the cold weather.
The cold weather can cause the blood vessels in your fingers to tighten up and shrink which causes a loss of blood flow to your fingers.
When you don't have enough blood flow to your fingers then the fingers can naturally swell and even go numb and stiff.
Also sometimes when your fingers warm up the blood vessels can break a little allowing some blood to flow into the tissues and cause the fingers to swell up.
There's usually nothing to worry about as the blood vessels will usually heal on their own but if the fingers don't stop swelling then seeing a doctor or going to the emergency room or urgent care would be a good idea.
The swelling and cold weather on the fingers can also cause Chilblains on your fingers and even toes.