The Flathub change is fairly recent. Until last month or so, only the ESR was available, and that was org.mozilla.Thunderbird with an uppercase T. Then that name was retired, and now we have the setup you show there.
Maybe Fedora will ultimately follow this. However, changing the name isn’t friction-free - flatpak update (and the GUI software managers) could transitioned you automatically from org.mozilla.Thunderbird to org.mozilla.thunderbird_esr, but didn’t rename the directory in ~/.var/app to match the new app name. So if you didn’t figure out that you needed to do that, you apparently lost your data.
I found from experience that flatpak update doesn’t handle renaming of ~/.var/app/org.mozilla.Thunderbird for you. So there’s no actual data loss, but it looks like there is, until you realise what has happened.
It would be good for Mozilla to mention this on the page really.