1. "Outdoor air typically has less than 400 ppm of carbon dioxide."

When he stated that from the get go, I knew he didn't know what he was talking about. CO2 levels have not been less than 400 ppm outside in over 7 years. Latest is above 420 ppm and climbing higher every year. If you are writing an article about the significance of the CO2 number.......at least get the baseline reading, that every scientist on the planet knows, right. Seriously, when I read less than 400, I immediately knew he knew  nothing about CO2 and was a reporter pretending he did by searching for things on the internet that lacked fact checking.

https://www.co2.earth/daily-co2

2. He makes assumptions that are misleading.  The most critical factor is your distance away from an infected person and whether anybody is wearing a mask.  I couldn't get the article to see if he elaborated that but his headline says the opposite.
3. Home CO2 meters are sometimes not calibrated well and can be off a great deal. I'm sure that his did a good job showing the change from the low outside of the plane and the higher level inside the plane.
4.  He is obviously correct that high CO2 is CAUSED by the lack of ventilation inside. Generally speaking, with all other variables the same, it means a HIGHER RISK at those times but absolutely does not mean that's when he was exposed. There could be great ventilation and the person sitting next to him could have COVID and shedding massive amounts of virus.  Or poor ventilation and nobody near his seat had COVID.

Here's a good discussion with more elaboration. 

May 19, 2021 CO2 Sensors for COVID-19 Risk Mitigation
National Collaborating Centre for Environmental Health 1
Indoor CO2 Sensors for COVID-19 Risk Mitigation: Current
Guidance and Limitations

https://ncceh.ca/sites/default/files/FINAL%20-%20Using%20Indoor%20CO2%20Sensors%20for%20COVID%20MAY%2017%202021.pdf