Players are able to consistently walk-over one block gaps (Meaning not by jumping, sprinting, falling to a lower block or riding/being helped by a mob/entity).
So far can be replicated randomly just by walking-over one block gaps.
Specific technique used cannot be determined properly for as stated before we're just "random luck" and therefore having no proper methodology.
Admittedly however, takes a some-what specific but achievable set of environments to properly reproduce but, it is proven to be 100% possible with in the game.