Thunderbird update, working and not working

I am using Thunderbird Portable as stand-alone installed on hard disk.

For years I have updated on the Help/About Mozilla Thunderbird page. Today I noticed that I was on version 91.1.x and the button said [Update to 91.1.y]. The thing is that I knew the current version was v102, meaning that the updater on the "About Mozilla Thunderbird" page was not working, or was only offering to update to a minor version that was still months out of date.

I ran the portable launcher which first updated the portable launcher then it updated Thunderbird Portable from v91.1.x to v102.2.0.

All is well, but why would the portable launcher successfully update Thunderbird when Thunderbird would not update itself?