I am being prompted for a passcode on my “other iPad” I only have one apple device… what is happening

Didn't you have another ipad in the years before?

If not so, check on appleid.apple.com which devices are linked to your Apple ID

See this on how to do that

1. Sign in to appleid.apple.com,* then select Devices.
2. If you don’t see your devices right away, click View Details and answer your security questions.
3. Click any device name to view that device's information, such as the device model, serial number, OS version, and whether it's a trusted device that can be used to receive Apple ID verification codes. The information might vary depending on the device type.

If you see devices you don't regognize please see this link and follow the instructions provided

If you think your Apple ID has been compromised – Apple Support (UK)