A guid isn’t a user id, if it is in this case, it’s an abuse of how guid is used, at least colloquially. I haven’t read enough to understand if it is user / machine id, I.e. only globally unique in the sense it’s a globally unique entity identifier.

Microsoft Can Track Users via a Windows Device ID https://news.ycombinator.com/item?id=48815196

Microsoft GDID telemetry includes full browsing and gaming history https://news.ycombinator.com/item?id=48787239

They stated the GUID is used to identify the prompt used to generate the image. How are you confused as to not being able to identify the user?

"I haven’t read enough to understand". Oh, now I know the answer to my question