Looks like ink to me. I reconcile my work bank statements on airplanes to keep busy/pass time and I use a red pen. My hand always looks like that in those exact spots at the end of the flight. The pressure up there must make the ink seep out a bit.
The older I get, the less I notice a minor scratch or cut. Plus with less collagen, it’s easier to do so. He had a little cut and didn’t know it is the most likely explanation (plus it’s what his people said happened).