Full sized school buses are often exempt/don't have seat belts due to their massive size and weight. Compartmentalization in school buses, in both mini and full size, is accomplished by high backed, well padded on all sides/surfaces, closely spaced seats. Also, at least here in Canada and I imagine as well in the United States, school bus standards (full and mini sized) include requirements such as smooth ceiling/walls with no sharp edges, windows designed with the horizontal centre bar to prevent ejection through the window, strength standards for the windows and frames, doors and frames for the same reason.
Back to the closely spaced and padded seats, the idea being a child seated correctly will remain in their "compartment" in a frontal collision and only strike padded surfaces. Due to their heads being proportionally heavier, this is not as protective for children under 40 pounds and they are recommended to be in 5 point restraints by many transportation groups, school districts etc.
Now as previously stated the seats on the shuttle bus above are most certainly not as closely spaced as school bus seats, and certainly the seat backs are not padded in the way school bus seats are to absorb impact. As well the windows are huge, not specially designed to prevent ejection like on a school bus. So personally I most certainly would not consider this to be on the same level as a school bus.