Access via a network to the computer is pretty clearly communications security. When the storage computer's fine-grained access control gets a request from the network, and itself goes to a authentication/credentials server (RADIUS, Kerberos) to see if the user has access to the data, it gets fairly blurred. To use your example, the data isn't in motion, but both access and the access authorization are.
Here you are describing access to the information, nothing is communicated. So that is just information security. Though if you are pedantic, the access keys must be transmitted so there is a communication of data in order to authenticate access rights.
But take the next step, after the system authorises the access, the data that was held security has to transmitted across the network without being intercepted or blocked. That part is communication security.
So we have two, maybe three distinct articles here. One on securing static data, one on authentication access to data, and a third on secure transmission or communication.