Any way this isn't a crack?

I have seen that sort of transverse "crack" develop when atmospheric moisture, condensed in a cylinder that had open to atmosphere valves, and sat in the cylinder over a long period of time. Granted I have only seen it in a V8; but a slanty is half a V12 right?. The moisture etched the wall, and it looked like a crack, and I could even sorta catch a fingernail in it, cuz metal was in fact missing. But it wasn't a crack.
I have seen what happens to a cylinder when water freezes in the jacket, and the frost-plugs didn't pop. And it can be ugly. Your crack, if it is a crack, ain't that kindof crack. So what kind of crack could it be? That left everything else intact?
IMO, it's too far down to affect the engine performance in any way. As soon as the head is back on, you can pressure test both the cylinder and the cooling system, and see what's what. And all it costs you if you don't fully torque the headbolts, is time. And not even a whole lot of that.