Yeah I have no idea on this one, looking at the footage frame by frame only confused me further. What I think is going on is that the zip is somehow allowing the hitbox and sprite to be desynced, letting the hitbox clip into the goal for a frame while the sprite keeps going up and out. Then when the goal-activation/level-transition animation plays a few frames later, the sprite is sucked back down on the y axis to match the hitbox (why not the x axis idk). Best I can tell the trick to hitting this as opposed to just popping out is to have the left and up presses either on the same frame or possibly one apart, and to start the zip as low on the wall as possible, as starting it too high up always hits the (equally weird but useless) horizontal zip through the scale.

Also I'll leave it up to whoever reviews this to decide how to retime it when the sprite never actually overlaps the goal, I just kinda eyeballed it based on my theory above

Mod Note: I just went by first frame he zips through the floor to the top, the end level sound plays when the player zips through the floor.