Portable Thunderbird No More Portable Than Mainstream Thunderbird?

Before I heard of Portable Thunderbird I tried -- successfully but not enough for me -- to do this myself using mainstream Thunderbird and just inputting the removable drive as the installation directory.

This was a Windows 10 Dell laptop that had had the previous installation of Thunderbird on its C: drive deleted, including ALL Mozilla/Thunderbird directories. The removable drive (D:) was an SDHC.

The new Thunderbird was 78.2.2 and the custom install settings were:

Install Location D:\Mozilla Thunderbird\
Install Maintenance Service

I used the Thunderbird Profile Manager to create a profile directory on the D: drive as well -- D:\username\AppData\Roaming\Thunderbird\Profiles\code.default\ -- and copied in the contents of the old Thunderbird profile.

I then ran Thunderbird and it worked perfectly, appearing just as it was in the old Thunderbird.

However, I found that these directories on the C: drive had been recreated:

C:\Users\username\AppData\Local\Thunderbird\ [empty]
C:\Users\username\AppData\LocalLow\Mozilla\ [empty]
C:\Users\username\AppData\Roaming\Thunderbird\ [not empty]
C:\Users\username\AppData\Roaming\Mozilla\ [not empty]
C:\Program Files (x86)\Mozilla Maintenance Service\ [not empty]
C:\ProgramData\Mozilla\ [not empty]

While these directories don't seem to contain personal data, they do contain update, extensions, and settings data. To a hacker these could be even more useful than personal data -- just hack the program code to send emails to them as well. All these directories should be on the removable drive too.

After a little research to fix this I came across Portable Thunderbird. I downloaded and installed ThunderbirdPortable 78.3.1 into D:\username\ThunderbirdPortable\. I created D:\username\ThunderbirdPortable\Data\profile\ and copied the contents of the last profile into it.

I ran ThunderbirdPortable.exe and it worked perfectly, appearing just as it was in the last Thunderbird.

I immediately checked and none of the recreated directories listed above existed.

But then I did Help -> About Thunderbird. This showed Thunderbird, not Portable Thunderbird, and version 78.3.1, but automatically did an update to version 78.3.2.

I then checked and found:

C:\Users\username\AppData\Roaming\Thunderbird\
C:\Users\username\AppData\Roaming\Mozilla\
C:\ProgramData\Mozilla\

So my question is: should Portable Thunderbird not be updated like mainstream Thunderbird, making the automatic such update in Help -> About Thunderbird a bug?

Or are these C: directories supposed to exist in Portable Thunderbird, making it not much more portable than mainstream Thunderbird?