Article is light on the details, but I think they're underplaying how quickly this is happening. BYD in China is building 6k electric buses every six weeks [1] (and this was as of a year ago, I believe they're building them even faster as of Oct 2019), which is enough to replace London's entire fleet. Bloomberg BNEF predicts at least half of buses in the world will be electric by 2025. Unlike electric cars, heavy duty vehicles consume much more fuel per mile, making the ROI on electric versions that much faster.

[1] https://www.sierraclub.org/sierra/when-it-comes-electric-bus...