That is pretty rare though. I live in Sweden (not the northern part) and at my previous job I liked to take walks at lunch and as long as it is not snowing, raining or being too windy it is pretty nice even at colder temperatures.

Now I'm usually talking about over -10C (14F) but a lot of people seem to think even that is too cold but just don't wear proper clothing.

I think that "certain temperature" varies for different people, or even over time for any particular person. When I was a child the cold killed me. A few weeks ago, the highs were in the mid-teens all week around here, and I found myself completely comfortable in jeans, a sweater, hat, gloves, and a coat while outside doing farm work. The big problem at those temperatures is working up a sweat when wearing clothes that don't immediately wick it away from the body. That gets very cold quickly.

I feel like he's thinking of 14 Celsius, not Fahrenheit

It's all relative. After a couple weeks of waking up to temperatures around or below 0F, the rise to the mid-teens felt like an early Spring.