McCoy's concern hits Luke harder than he expects. He knows the man feels things strongly, but he hadn't quite realised how much he had relaxed his own shields as they talked until he feels the wave of worry, ebbing and building like the start of a sandstorm.

"Oh, no. No. I mean, a little, but that was before I had my Jedi training. Now... well, I'm the last Jedi. So it sort of falls to me to do what the Order used to. Whatever that is. I'm still trying to find that out." he gives a small, sad smile. "I wasn't governmental military most of my service. We were the Rebellion. I was a rebel fighter and pilot."

McCoy probably still has good reason to worry. Luke is just young enough to not really see that.