Even with the same phone, if you add several items, they will each have their own unique id. I think the fingerprint icon might be a little deceptive here. Like I said before, UniqueID is used to assign a unique ID to just about anything. It it not a unique identifer for a logged in user. It can be, but only if you design the app like I indicated above. The unique id is a value that can never be duplicated (look up the definition of UUID or GUID).
In your case, the only thing that would ensure complete privacy would be some sort of hashing or encryption, which isn’t provided by Glide or Google Sheets at this time.
Here are a couple of posts that illustrate how I plan to implement Unique ID in my project.