My theory for how that happened:
I guess you stopped pedaling at some point in time.
Your belt became a bit loose because the freewheel is worn already (but not that much).
Anyway, the diameter of the freewheel decreased (a little bit) and that generates more play, that was the reason for the belt to start skipping teeth.
At the moment when the first tooth got stuck between the snubber and the freewheel - while the rear wheel was still turning - the tooth was ripped off immediately.
(Possibly you felt some kind of kickback at the pedals?)
So, I think that the belt’s teeth were sheared off by the freewheel’s teeth.
To mount a new belt properly you must open the big groove nut at the left side of the bottom bracket, too! Opening only the bolt 274, at the underside of the bottom bracket, is not sufficient.
You need a Ø 60 mm hook key.
Treating the belt with a screwdriver, as the Strida manual suggests, is nothing but wrong btw!
There is no maintenance-free bike existent in this world - but dubious marketing claims are present everywhere!
The belt itself is maintenance-free, but belt tension has to be observed according to mileage.
(I guess you never increased it within five years?)
Next, you should figure out what’s rubbing 