I want to say maybe two people got into it in between the two SUVs, but being there's no appearently sheet metal damage that's not a conclusion.
Another possibility is they're hating cause neither are parked properly in your spaces. In any case, that's beef between the two owners. Lastly, maybe a bunch of f*wad teens trying to be "cool" vandalizing another's property. The East Bay had a random string of vehicles getting their tires slashed.
Vandals, theives or anyone with criminal intent don't care nor will think twice of judgement day.
Either way I feel bad for your loss and whoever did it will get what's coming to them in due time.