How many people live less than 19 minutes from the train station? Of course it's valid. No the cyclist wasn't in work clothes because they like to show "hey look a cyclist" in the photos. Of course the cyclist wins even with changing. Plus what happens to the train person if they are 5 or 10 minutes late, leaving or arriving at the office? They end up taking 30 mins maybe even 1 hour longer after waiting for the next train. Don't know why you think train is better than cycliing for such a short journey? It's madness not to cycle when it's only 6 miles. You'll have people getting a taxi instead of a 2 mile walk next.
I have offered no opinion as to whether train is better than cycling. What I have said is that as a comparative test, this test is flawed in many ways, and if the conclusion of the test was to determine the quickest way to get to work from point A to point B, there is no real difference between Train and Cycle. One could even argue that due to the 20 minute walk, the train passenger is getting some exercise. In presenting the cyclist as being significantly quicker, the narrative is false. Only the Bus is ineffective as a method for undertaking the tested journey. Car is ineffective if the commuter must travel at the busiest peak time.
And re-reading the article, the write up is contradictory nonsense anyway. The article says everyone sets off at 08:00, but she says she sets off at 8.15am. Somehow she just misses the 8.08 service and gets the 8.26 despite arriving at the station at 8.24 (9 minute walk according to google maps)! Having arrived at 8.41 it then for some reason takes her 23 minutes to do the 10 minute walk from the station to her office. She also records that her cycling colleague arrived at the office at 08:41 making the trip in 26 minutes, which suggests that he also set off at 8.15 and not 8am as listed at the start of the article. So if the train passenger hadn't stopped for a chat and coffee she would have arrived at 8.48, only 9 minutes after the cyclist who is still in his lycra at his recorded finish time.