He did it exactly like I do. There's little risk. The cut into the pit is done with the momentum of the (light) knife, not by pressing on it with your muscles. In the unlikely event that the knife missed the avocado altogether, it would be unlikely to cause much damage.
Who cares about the neatness of avocado slices? I do. Presentation of food is important to me.
I whack the pit against the inside of the sink to free the pit from the knife, rather than the reverse finger squeeze.