New alert: “Device Added to Your Account”

Hello,

I’ve looked around a bit to see if this question has already been asked but I’ve only found questions with similar but not identical alerts being received.

Early this morning I received an alert on my iPad saying:

“Device Added to Your Account

An iPhone now has access to iMessage. If you recently signed in to this device, you can ignore this notification.”

I haven’t added any new devices to my account so I checked in my settings to see if there were any unfamiliar devices linked to my Apple ID but I only found my own devices listed. I changed my Apple ID password and device passcodes anyway. Then I checked my iCloud account on a web browser and there was another device listed in Find My apart from my current devices, but it had my name on it so I think it’s just my old phone which I erased a while ago (but apparently didn’t remove from Find My. I guess you have to do that separately?)

I messaged Apple Support to see if I could find out what the alert was about but aside from telling me that the security measures I took were enough to keep my account secure, there wasn’t much else they could tell me.

It’s bugging me not knowing what caused the alert and I don’t know if it’s something I should look into more, or just disregard and not worry about. Has anyone else received the same alert and do you know what might’ve brought it on?

Thank you for your time