It is a message indicating that your device is associated with another Apple ID. That means that someone other than you was signed into your device yesterday, and had one of the following occur while they were signed in:
- Subscribed to iTunes Match
- Subscribed to Apple Music
- Turned on Automatic Downloads
- Joined a Family Sharing group
- Downloaded a past purchase
Here is a support article that explains associated devices: Associated Device.
Did you let someone else sign into your device yesterday?
Best,
GB