Video here. Joe Biden is seen bringing his bicycle to a stop, placing his left foot on the ground, tilting to the right, then falling. It's clear what happened. He couldn't disengage his right foot from the stirrup on the peddle.
Stirrups on bike peddles? That's what you call an accident waiting to happen. It's almost as if one of his handlers wanted him to fall.
Get a trike, Joe. Bikes are for kids under 75.