It depends on the shape of the terrain and the position of the player and Sculk Shrieker, but sometimes Wardens can fall while emerging, or perhaps more specifically, can emerge in locations that make them fall by themselves, which looks very unnatural. 

Players digging blocks under it is inevitable, but I expected it to be able to always be able pick a spot where this doesn't happen naturally without outside influence.

It seems to occur when the Warden tries to emerge from the side of a Sculk block that has its top covered, or perhaps from sculk veins? I'm unsure exactly