When the intruder looks at the transmitted data and finds information about the sender and the receiver of the data or other peripheral information that won't help him hack the system but know more about the transmitted data type/nature/ sender and receiver peripheral info.
What you describe isn't technically an attack. Nothing is exposed, nothing is exploited, and the parties involved are not affected.
What you are describing is a phase of an attack called "Information gathering". Any targeted attack will involve Info Gathering at some point so that the attacker knows what to do to gain what is desired (DoS, access, data, etc.)