Where did you get the impression that two is fine? I am somewhat familiar with the issue, and looked at both of your links, but still don't understand. Where I live, they stack containers six high.
That part was a joke because of Flexport's layoffs due to lack of volume. The stacking is probably a separate topic compared to the success of his business, but was just stating why his name and company are familiar on HN.
I personally believe they should stack them vertically vs horizontal stacking to save space so they are always accessible vs 2-3-4 high. (also a joke)
[1] https://www.npr.org/2021/11/03/1051773672/a-look-at-whats-ca...