I worked at Amazon recently as a retirement job operating all of the different warehouse equipment. All of the equipment at this warehouse was liquid hydrogen powered so I know it is highly flammable, but being contained as it is it’s safe enough to use as fuel. An e-bike filled with liquid hydrogen just might have a crash that causes a spark setting off one hell of an explosion.
Unlikely? Maybe... Maybe not, only time will tell.
As somebody earlier pointed out, we’ve used hydrogen vehicles for about 150 years and there has been no explosions, Hindenburg aside.
From my research, you need an ignition source for their to be a risk or else it just combines with oxygen in the air almost instantaneously.