I recently glued up a panel from pine boards. I decided to try
smoothing the end grain with my new Veritas low angle jack plane. Did
an okay job, but not as well as I hoped (probably my technique).

Anyways, when I was done I noticed a series of distinct scratches down
the sole of the plane that hadn't been there before, as well as a number
of nicks in my (newly honed) blade. A certain amount of foul language
ensued...

Any ideas what might have caused this or how to avoid it in the future?

My current theory is an errant grain of something abrasive (sand?)
embedded in the wood.

Chris