The figures given in on the site are taken from actual usage and so include the fact that buses tend to stop and go more than trains, are less likely to be full, etc. That's a useful view but it's good to look at the physics based maximum efficiency when full view too. I really, really recommend Sustainable Energy Without the Hot Air[1] for getting a good sense of the numbers right now the chart on vehicle efficiencies[2]

[1]https://www.withouthotair.com/

[2]https://www.withouthotair.com/c20/page_128.shtml