Having noticed a similar effect, I have a theory about that.
I have both chronic bronchitis and advanced emphysema, and I find that I can breathe much easier in cold weather. Having been something of a racer back in the day, I can't help but suspect that it's based upon the same principle as a car running better in cold or foggy air. It's a denser intake charge.
A 'normal' person with nasal congestion is sort of in the same predicament that I am all of the time, in that inhalation is difficult. Warm air takes up more space per molecule than does cold air. In made-up numbers, rather than actual figures, let's assume that your lungs hold 1 litre of air each. With cold air, you might have something like 30% more molecules (and therefore 30% more oxygen) per breath than you do with warm air. As a general rule (at least where I live), it's warmer inside than outside.
Also, in an enclosed environment the air will have a lower percent of oxygen since carbon dioxide will accumulate without the benefit of free circulation.