They are SMS messages sent from those numbers to your RingCentral number. You need to login your RingCentral account (https://service.ringcentral.com) and add those numbers as your personal contacts.
However, right now, only the RingCentral mobile app takes the Personal contact. Thus, once a number is added to your RingCentral personal contact, you will see the name of that person instead of the phone number on your RingCentral mobile app.
For some reason, the RingCentral desktop (Mac OS and Windows) app does not take the Personal contact and that is why it just shows the phone number. I will check with the dev team to see how to fix this and make it available in the next release.