I knew that the cheaper seatposts used insertions, but that's the first time I've seen one fall off like that.
I have a Bontrager zero-setback post and a Post Moderne (Trek's house brand) that have their heads press fit into the post but neither have shown any signs of looseness in tens of thousands of miles.
I believe current American Classic seatposts are also a two-piece press fit but my older one (1996) has a one piece post and lower clamp.