I agree, you handled the situation well.
It's funny sometimes how an umpire will know what the coach means to do better than the coach.
If a substitution is obviously situational and I have a sense there will be a re-entry or follow-up change, I will make a concerted effort to make eye contact with the coach at the end of the half-inning. I don't say anything, but some of these coaches have so much going on in there (leave it alone
), sometimes just seeing you look at them will make that light bulb come on. If there is no effort to make a change, I let it go and move on with the game.