6km one-way isn't very remarkable here indeed, in terms of distance I would consider it a short bike ride. I'm cycling ~8km each day myself now, but I have colleagues who do ~15km one-way each day, which I would consider on the high end for a bike commute.
I agree with the sentiment of the article though, which is that cycling to work basically has only advantages if the weather is good. When it's raining or particularly windy I still take the car, but on all other days I greatly prefer cycling. No traffic, no problems finding a parking spot, it wakes you up in the morning, makes you hungry (in a good way), saves money, and for me it basically eliminates the need to allocate any extra time for additional exercise.