Tight snap fit bayonet type attachment point.
Can be added to any surface, as part of the design, to attach two things together.
If used separately, the top rotates on the bottom.
Will take direct pulling (on the axis) to get them apart.
One end of the top has a larger diameter so this will only fit in one direction.
Scale this up for larger fixture. Scaling this up increases the force needed to separate the top and bottom.
I looked at the little rotating top of a small electronics screwdriver.