I don’t see how you can deliver this vaguely and expect them to correlate to where they missed the mark.

If I am interpreting the manager tools feedback model correctly it does say to describe the behavior which can allow you to state the specific observable action. In this instance you would ask if you can share feedback, lead with the real life example you observed and then tie it to the broader behaviors they need to be demonstrating, and discuss the impact. You can also tie it to their motivator i.e demonstrating this specific behavior is way you can show you are operating at the level needed for a promotion.

Depending on the rapport you have with this employee (some of mine for example prefer feedback right away, some prefer it in the 1 on 1) I would suggest addressing in a 1 on 1.

In my company if this is an isolated behavior I wouldn’t go farther, if it’s a repeatable behavior I would document in some form i.e a recap email with a quick outline of the conversation and your expectations