Good morning, afternoon, or evening fellow GrapheneOS users.
I posted this question in the Matrix server, but it got a bit buried, so I figured I would do so here as well. I'm hoping to better understand what data is shared between a guest user and the owner user.

The scenario that prompted this question is as follows.
I wanted to make a Japanese google play account, so I:

Made a guest user, using the "install available apps" option to install ProtonVPN, which I use on my owner profile. The delete guest activity option was set to True.
Switched to the guest profile. During setup, I set the system language to Japanese. I wasn't sure if doing so would matter, but I figured I might as well.
I plugged in the phone to my computer and moved a couple text files to the download folder.
I logged in to ProtonVPN and VPN'd to Japan
I then, with the VPN active, installed Google Play Services from the "apps" app, as I wanted to be able to quickly check that I could download Japanese apps.
I finally used the "accounts" page in settings to make a Google account. It worked fine, and I confirmed I was able to download Japanese Google Play apps.

I then closed the guest user, which I assumed would delete all data, as the delete guest activity option was set to True. But when I returned to my Owner user, I noticed that: (1) The Google Play Store (2) Google Play Games (3) Google Messages (4) and Simple Gallery (not a Google app) had their application names in Japanese in the app drawer and home page.

This was peculiar. (1) None of the files I moved over on the guest user were still there; (2) the account I made in the guest user was gone; (3) my owner user's language settings remained "English"; (4) I never installed Play Games, Simple Gallery, or Google Messages on the guest profile--only the Play Store; (5) none of the Apps' UIs were in Japanese, and their dedicated "info" pages and the app list in settings both showed their names in English. And yet, on the home screen and in the app drawer, their names appeared in Japanese.

Restarting the phone, creating a new guest user with the language set to English, clearing cache, none of that would reset their names to English. Disabling and re enabling the apps did reset their names to English.

So all in all, I'm wondering what exactly occurred here. It's clear that the data from my guest profile was properly wiped, as the files, accounts, etc. did not persist. But it is also the case that some data of some sort must have crossed over between user profiles, because I experienced this strange phenomenon with the names of those select few applications.

I was under the impression until now that nothing you do in a guest profile should impact your owner profile, but after this experience, I was hoping someone could clarify for me what exactly crosses between user profiles and what does not.

Thanks a bunch!