I think both (salty moist air + bimetal contact) and add potential bad design and cost cutting (or poor quality control) in production/materials…all of this mixed with a student driver and sub-standard dealer support as catalyst.
Corrosion on the hubs likely classic galvanic corrosion (assuming steel hub and aluminium wheel). Maybe the severity could make one infer that the car spent most of the time outside and/or was not washed often to remove the electrolyte (how often does the average student wash a car?). What stupid things do students often do with their cars? (hold my beer…)
But the corrosion around the door handles and window seal could also indicate poor design/manufacture. Do the door seals maybe trap water and keep metal parts in essence submerged in water? (in a coastal area salty deposit mixed with rain water 2 weeks later running into every small nook and cranny but can all the water exit again?).
Quality of parts supplied to manufacturer. They possibly ordered galvanized bolts/nuts…but is that what they received? (the bean counters need the car produced as cheap as possible, so a cheaper bolt supplier was used?)
Rusted wheel nuts. Were tyres ever replaced/brakes serviced? (did tyre place or servicing agent apply anti-seize grease etc.).
Poor dealer/servicing standard. The servicing dealer did not notice the corrosion so that corrective steps could be taken sooner?
I must admit I first had to google galvanic corrosion. Found the following two pdf docs quite interesting/useful: Types of corrosion (stray current corrosion possibly relevant for the PV guys?) . Galavinic corrosion fairly detailed overview.