It is empirical evidence at best. There is nothing rigorous about it.
Considering this is what they do for a living, I doubt they would get something as easy as 30fps to 60fps wrong, he played the game for a good 15 minutes and said it occasionally drops below 30fps, plus with the pc he built it shows that it would be impossible for switch to run it ay 60fps, even with the lowest settings, cause of the cpu.