I suspect it is the same for the other percentages thrown around on that diagram. ... and why doesn't the H2 vehicle do regenerative braking?
This is applied to all steps, electrolysis, compression, transport, and fuel cell conversion back to electricity.
Current fuel cells cannot put out enough burst power to acceleration nor can they accept electricity in reverse to generate hydrogen so all current fuel cell vehicles use a traction battery that is charged by the fuel cell, they are basically series hybrids. They also typically have lower acceleration because the small traction battery + fuel cell cannot supply as much power as a much larger full EV battery.