Ok, so the paint/powder was good at one time.

If the seatstay is loose, I would think you should be able to feel or see it move, as well as seeing cracks penetrating all the way through. Perhaps put your thumb on the seatstay and seattube, and see if you can feel any movement when you try to move it (within reason).

Also, if the rear-end remains aligned, then that would support the assumption of no damage. from the partial fall.

Any more photos of that stay, pre-powder?

To me that left stay just looks chunkier than the right stay, post powder.

I think you may have had excess powder build-up on that left side that has partly flaked off for some reason.