One word with two distinct meanings. In CTF parlance a “flag” is a goal or a proof: typically some text that you can only see if you achieve some goal. In this lab. the “flag” is the text you see when you look at the application layer.
In TCP parlance a “flag” is something used in the protocol to manage or indicate the connection state.
Perhaps changing the request from “find the flag” to “find the message in the application layer” might be better/clearer?
