How to tell a Scratch from a Crack in a Cylinder?
Don't think so, too deep.
OP is rebuilding after a previous owner already rebuilt.
The previous builder could have easily left a burr, or done other dumb stuff to the rings to cause it.
At the same time, I've seen similar when someone drags the rods and pistons out of a motor. A sharp edge can catch and cut a surprisingly deep gouge.
Also a million other things which could cause it. Keep it clean during reassembly and it probably won't cause a problem. The alternative is boring it, and if that's not in the budget then it's a moot point. Plus, plenty of half decent used engines probably have similar levels of damage and run just fine.
Heck, Porsches are known for cylinder scoring and they still make good power even with significant damage... I wouldn't lose sleep over one little racing stripe in the bore.