I'm the parent commenter. No, it doesn't make a difference in this case. The "mark as unread" feature in every chat program takes less time to use than it does to tell someone to paste the same text they've already written into an email. The time it takes to ask is effectively time lost on the CTO's part, and the time it takes to resend the message via email is time lost on the worker's part.
If the CTO wants to convey the message that, in the future, such requests should come through email in the first place, it's still better to wait, then respond through Slack, and then leave a note about protocol in the future. Why is it better? Because they're leaving this note when they aren't so busy, rather than interrupting whatever they were doing to write it.
If the CTO wants to convey the message that, in the future, such requests should come through email in the first place, it's still better to wait, then respond through Slack, and then leave a note about protocol in the future. Why is it better? Because they're leaving this note when they aren't so busy, rather than interrupting whatever they were doing to write it.