Notices a zig zag scratch on my seatpost.
Coin test sounds all the same, I’m wondering if it could just be the pressure from my bike stand clamp cracking the paint when I was working on the bike?
Hard to tell with all the stuff reflecting in the shot. However, "just the pressure" is the thing you should be worried about. Paint cracking from the carbon below deforming elastically is a thing that can happen, but usually warrants a closer look to say the very least.
However, superficial scratches (as is often the case with ziagzagging from twisting a seat post in a seat tube) are usually just cosmetic.
try to do the coin test
It already says in his post that he did, no?
