Back wheel is locked up

I wouldn't think a bearing would seize that quickly; they are sealed bearings, so even salty air would take a long time to penetrate.
I'd check the brakes first; one can't tell at a glance whether disc brakes are locked up. Is something pulling on the cable?
Do let us know what it was, once you've figured it out.
I have not been inside one other than other folks pictures, but in a geared hub motor could one or more of the gears get damaged or loose and cause it to jam up? Looks pretty tight inside…I agree with Smaug, typically bearings don’t seize at once.