Interesting our assumptions...
I VERY rarely work slowpitch, so assumed the question was about fast pitch. If R1 is stealing in fastpitch, and the batter catches the ball, you definitely have a possible interference call.
You work slowpitch - so you assumed he was talking about slowpitch. Since runner can't run until the ball crosses the plate, he couldn't already be running when the ball was caught... so I definitely see your point that the right call is simple dead ball - ball. (Similar to my comment - if not stealing, I have nothing, no play to interfere with).