I have always been a little wary of Apple Wallet, because the Apple documentation is so sparse. It doesn't address some fundamental questions, such as whether the wallet is associated with the iPhone or Apple ID.
Why do I care about this? Well, I know I can login to a primary Apple ID on an iPhone, and various data will be associated with the Apple ID. Some of it may be synchronised also, e.g., iCloud documents. "Find my ..", Safari bookmarks, etc., may be synchronised too. And I know that in some cases, like the App Store, you can login with a different Apple ID and it uses that app, associated with that other Apple ID.
It appeared that Apple Wallet might be different, as there doesn't seem to be the option to associate it with a different Apple ID in the same way that you can do that for App Store. However, I just noticed that my personal phone contains passes in its Apple Wallet that were definitely not from me. I suspect this may have been from some time in the past when I logged in to a shared company Apple ID, but now I'm worried that the sharing may have gone the other way around too, and my credit card may now be available for use on other devices that happened to login to that shared company Apple ID?
Or it may be that payment cards are treated separately from the rest of the passes in the Apple Wallet? (so only passes get shared in the manner described above?)