That does sound concerning. It's unusual for an unknown device to appear in your Find My Device feature if it's not associated with your Apple ID or logged in with your credentials. Here are a few possibilities:
1. **Shared Account:** If someone else has access to your Apple ID or was previously logged in with it on another device, it might appear in your Find My Device list.
2. **Previous Device:** It's possible that this unknown device was previously logged in with your Apple ID, even if it's not currently logged in.
3. **Synced Accounts:** If you use iCloud Family Sharing or have any other shared services, a device from a family member might appear in your Find My Device list.
To ensure the security of your account:
1. **Change Password:** Consider changing your Apple ID password immediately. This action helps prevent unauthorized access to your account.
2. **Review Connected Devices:** Check all devices linked to your Apple ID via the Apple ID settings. Remove any unknown or unrecognized devices.
3. **Enable Two-Factor Authentication:** If you haven't already, enable two-factor authentication for an added layer of security.
4. **Contact Apple Support:** If you're certain the device shouldn't be associated with your account and it's causing concern, contact Apple Support. They can help investigate and ensure the security of your account.
Regularly reviewing your connected devices and maintaining strong security measures can help keep your Apple ID and devices secure.