Thunderbird Portable or is it?

My PC died so I transferred the backup drive to another system. But when I tried to run Thunderbird Portable (TBP) it told me to go f**k myself. Well it didn't say so literally and I can't recreate the issue with error as now if I try to open the backup it just refuses to open at all. It does show up in Task Manager for a bit but then just disappears.

So what I did next was to install a fresh copy of TBP add an email account and all that as I did want easy acces to my email account(s). But guess what showed up along side the one email account that I added to the freshly installed TBP... The email accounts that are in TBP hat was already on this system.

So should I be concluding that TBP isn't actually portable?

And if it has anything to do with the update function. You know you install TBP but after a wile it starts nagging about available (regular) updates and someone falls for it. Is it now a hybrid semi portable version. I didn't update the backup like that but the TBP on this other system sure got updated in such way at some point. Why is that update function not disabled in the portable version?