Earlier quoted context omitted.
It is including heavy vehicles, but also motorcycles. The average for "passenger vehicles" is still about 10.5 l/km. Just bigger cars I think. https://www.budgetdirect.com.au/car-insurance/research/avera...
Motorcycles, perhaps surprisingly, aren't all that much more efficient than regular gas cars. The tl;dr is that their aerodynamics are terrible, and their engines not tuned for fuel efficiency.
For example, https://afdc.energy.gov/data/10310 gives motorcycles as almost 2x as efficient as cars, almost 3x as efficient as "light truck / van".
Given that enormous amount of metal that's not being hauled around, I would have expected a bigger difference. Nonetheless, for single-occupant travel, halving transportation carbon footprint would be quite a great thing.